ALBINO, a biological term (Lat. albus, white), in the usual acceptation, for a pigmentless individual of a normally pigmented race. Among some flowering plants, however, the character has become one of specific rank, and among animals we have in the polar bear and the Greenland hare instances where partial albinism—for in them the eyes are black and other parts may be pigmented—has also become a specific character.
A true or complete albino is altogether devoid of pigment. One result of this among the Vertebrata is that the eyeball is pink in colour, since the cornea, iris and retina being transparent, the red blood contained in the capillaries is unmasked by the absence of pigmentary material. In man, and doubtless also in lower forms, the absence of this pigment produces the well-marked albinotic facies. This is a condition in which the eyelids are brought into a nearly closed position accompanied by blinking movements and a general wrinkling of the skin around the immediate neighbourhood of the eyes. It is the result of the too great intensity of the light incident upon the retina, and which in normal eyeballs is adequately diminished by the absorptive power of the pigmentary material.
In a complete albino not only is all pigment absent in the skin, but also that which is normally present in deeper organs, such as the sympathetic nervous system and in the substantia nigra of the brain. There is some reason to believe that a peculiar condition found in the majority of human albinoes, and known as nystagmus, is correlated with the absence of pigment in the central nervous system. This condition is one marked by unsteadiness—a sort of flickering rolling—of the eyeballs, and it becomes more marked as they endeavour to adjust their accommodation to near objects. It is thought to depend upon some connexion, not yet anatomically demonstrated, between the third cranial nerve and its nucleus in the floor of the iter and the substantia nigra.
In addition to complete albinism, there exist, however, various albinotic conditions in which more or less pigment may be present. Familiar instances of this partial albinism is seen in the domestic breed of Himalayan rabbits. In these animals the eyeball and the fur of the body are unpigmented, but the tips of the ear pinnae and extremities of the fore and hind limbs, together with the tail, are marked by more or less well defined colour. One remarkable feature of these animals is that for a few months after birth they are complete albinoes. Occasionally, however, some are born with a grey colour and a few may be quite black, but ultimately they attain their characteristic coat. There is some reason to believe, as we shall see later, that in spite of the presence of a little pigment and of occasional wholly pigmented young ones, Himalayans must be regarded as true albinoes. Other individual rabbits, but belonging to no particular breed, are similarly marked, but in addition the eyeballs are black. Some domesticated mice are entirely white with the exception that they have black eyeballs; and individuals of this type are known in which there is a reduction of pigment in the eyeballs, and since the colour of the blood is then partially visible these appear of a reddish-black colour. Such cases are interesting as representing the last step in the graded series through which the condition of complete pigmentation passes into that of complete albinism.
There is evidence, as shown by G. M. Allen, that partial albinism is a condition in which pigment is reduced around definite body centres, so that unpigmented areas occur between the pigment patches or at their borders. In the mouse, ten such centres may be distinguished, arranged symmetrically five on either side of the median plane—a cheek patch, neck patch, shoulder patch, side patch and rump patch. Various degrees in the reduction of the pigment patches up to that of complete elimination may be traced.
Some animals are wholly pigmented during the summer and autumn, but through the winter and spring they are in the condition of extreme partial albinism and become almost complete albinoes. Such instances are found in the Scotch blue hare (Lepus timidus), in the Norway hare, in the North American hare (L. americanus), in the arctic fox (Canis lagopus), in the stoat and ermine, and among birds, in the ptarmigan, and some other species of Lagopus. How the change from the autumnal to the winter condition takes place appears not to be definitely settled in all cases, and accurate observations are much to be desired. In the case of the Norway hare, it has been stated that a general moult, including all the hairs and under fur, takes place and new white hairs are substituted. The process of moulting is said to begin in the middle of autumn and is completed before the end of December, by which time the fur is in its winter condition, and is closer, fuller and longer than in summer (Naturalists’ Library, vol. vii.). On the other hand, it has been stated that during the whole of the transformation in the fur no hairs fall from the animal, and it is attributed to an actual change in the colour of the hair (Edinburgh Philosophical Journal, vol. xi. p. 191). In the case of the American hare, however, some very careful observations have been made by F. H. Welch. In this animal the long hairs (which form the pile) become white at their extremities, and in some of them this whiteness extends through their whole length. At the same time, new hairs begin to develop and to grow rapidly, and soon outstrip the hairs of the autumn pile. From their first appearance these new hairs are white and stiff, and they are confined to the sides and back of the body. It is not clear from Welch’s account what is the cause of the whiteness of the tips of the hairs of the autumn coat, but his figures suggest that it is due to the development of gas in the interspaces between the keratin bridges and trabeculae of the hairs. There is nothing to show whether the pigment persists or is absorbed. Probably it persists. In this event, the whiteness of the tips will be due to the scattering or irregular reflexion of the incident rays of light from the surface of the numerous gas bubbles. In the case of the ptarmigan the evidence is clear that the existing autumnal feathers do change, more or less completely, to white. But the evidence is not conclusive as to whether any part of the winter condition is additionally produced by moulting.
The condition of albinism thus assumed as a seasonal variation is never complete, for the eyes at least retain their pigmented state. The reason of this is readily understood when it is borne in mind how disadvantageous to the function of sight is the unpigmented condition of an albino’s eyeball; a disadvantage which would be probably much accentuated, in the cases now under consideration, by the bright glare from the surface of the snow, which forms the natural environment of these animals at the particular period of the year when the winter change occurs. In some cases, as in all the varying hares, in addition to the eyes retaining their normal pigmentation, areas similar in extent and situation to those on the Himalayan rabbits also retain their pigmentation; and in the ptarmigan there is a black band on each side of the head stretching forwards and backwards from the eyeball, and the outer tail feathers are black.
Albinism is restricted to no particular class of the animal kingdom; for partial albinism at least is known to occur in Coelentera, worms, Crustacea, Myriapoda, Coleoptera, Arachnida and fishes. The individuals in which this diminished pigmentation is found are for the most part those living in caves, and it is probable that their condition is not truly albinotic, but only temporary and due to the absence of the stimulus of light. This may be also true of some of those instances that have occurred among frogs, in Proteus, and with an axolotl once possessed by the present writer. This latter animal was quite white, with the exception of the black eyeballs. At the end of four weeks after it was first purchased the dorsal or upper surface of its external gills developed a small amount of dark pigment. Within the next few weeks this increased in quantity and the dorsal surface of the head and of the front end of the trunk began to be pigmented. The animal died at the end of the eighth week, but it is possible that had it lived it would have become wholly pigmented. But, apart from these instances, albinism is known, according to W. E. Castle, who cites it on the authority of Hugh M. Smith, to occur among a breed of albino trout, which breed true and are reared in the State fish-hatcheries of America. With birds and mammals, however, there is no doubt that complete albino individuals do occur; and among species which, like the jackdaw, certain deer and rabbits, are normally deeply pigmented.
Albinism occurs in all races of mankind, among mountainous as well as lowland dwellers. And, with man, as with other animals, it may be complete or partial. Instances of the latter condition are very common among the negroes of the United States and of South America, and in them assumes a piebald character, irregular white patches being scattered over the general black surface of the body. Occasionally the piebald patches tend to be symmetrically arranged, and sometimes the eyeballs are pigmentless (pink) and sometimes pigmented (black).
According to A. R. Gunn, of Edinburgh University, who has recently been investigating the subject of albinism in man, there is reason to believe that a condition of piebald albinism occurs also in Europeans (Scotsmen). He has examined subjects in which the whole of the hair of the body is white, but the eyeballs are pigmented, often deeply; and, conversely, he has seen cases in which the eyes are pink but the hair is pigmented. The hair and the eyes may be regarded as skin patches, in which sometimes the one and sometimes the other is pigmentless. He believes that, were it not for the generally very pale colour of white-skinned races, this piebald condition would be as manifest in them as in negroes, over the whole surface of the body.
In complete human albinoes, albinism is correlated, in addition to nystagmus, with a peculiar roughness of the skin, making it harsh to the touch. The skin is also milky-white in appearance.
According to C. J. Seligmann, there exists among the Papuans an albinotic race whose skin varies in colour from a pink-white to that of café au lait; the eyes are generally greenish, hazel or brown, and the hair is tow-coloured. The skin where unexposed is pinker than that of a normal North European. Like complete albinoes, this race suffers from photophobia, and is characterized by the albinotic facies.
Before we can inquire into the cause and meaning of albinism it will be necessary first to consider the nature Of pigmentation. It has recently been ascertained that the coloration of certain sponges is due to the interaction of an oxydizing ferment, tyrosinase, upon certain colourless chromogenic substances. In 1901, Otto v. Furth and Hugo Schneider showed that a tyrosinase could be obtained from the blood of certain insects, and, acting upon a chromogen present in the blood, converted it into a pigmentary substance of melanin-like nature. Hans Przibram also extracted a tyrosinase from the ink-sac of Sepia, and, causing it to act upon a watery solution of tyrosin, obtained a black pigment. From the blood of Bombyx mori, V. von Ducceshi has also obtained a tyrosinase.
Subsequently (1903) L. Cuénot, in order to explain certain features in the hereditary transmission of coat colour in mice, postulated the hypothesis that the grey colour of the wild mouse (which is known to be a compound of black, chocolate and yellow pigments) may be due either to the interaction of a single ferment and three chromogens, or vice versa, to one chromogenic substance and three ferments.
Since then (1904) Miss Florence Durham has shown that if the skins of young or embryonic mammals (rats, rabbits and guinea-pigs) be ground up and extracted in water, and the expressed juice be then incubated with solid tyrosin for twenty-four hours, with the addition of a very small amount of ferrous sulphate to act as an activator, a pigmentary substance is thrown down. The colour of this substance is that of the pigment in the skin or hairs of the animal used. Miss Durham interprets her results as indicating that the skin of these pigmented animals normally secretes one or more tyrosinases. The same result was obtained from the skins of some unhatched chickens. The skins of albinoes gave no results.
Not only have such results been obtained with sponges, Insects, cephalopods, birds and mammals, but Em. Bourquelot and G. Bertrand have shown that certain fungi, the tissues of which, when exposed to the air by injury, become immediately coloured, do so owing to the action of tyrosinase upon one or more chromogenous substances present in the plant. We may conceive, then, that a pigmented animal owes its colour to the power that certain tissues of its body possess to secrete both tyrosinases and chromogenic substances. And the period at which this process is most active is at birth, or preceding it or immediately succeeding it. In spite of the inquiry being only in its initial stages, there is already good evidence to believe that Cuénot’s theory is correct, and that an albino is an individual whose skin lacks the power to secrete either the ferment or the chromogen. It forms one but not both of these substances.
A moment’s consideration, however, will show that, while an albino may be an individual in which one or more of the complementary bodies of pigmentation are absent, a pigmented animal is something more than an individual which carries all the factors necessary for the development of colour. For it must be borne in mind that animals are not only coloured but the colour is arranged in a more or less definite pattern. The wild mouse, rat and rabbit are self-coloured, but the domesticated forms include various piebald patterns, such as spotted forms among mice, and the familiar black and white hooded and dorsal-striped pattern of some tame rats.
Colour, therefore, must be correlated with some determinant (determining factor) for pattern, and it cannot, therefore, exist alone in an animal’s coat. And we must conceive that each kind of pattern—the self, the spotted, the striped, the hooded and all others—has its own special determinant. Given the presence of all the necessary determinants for the development of pigment in a mammal’s coat, some or all of the hairs may bear this pigment according to the pattern determinants, or absence of pattern determinants, which the cells of the hair papillae carry. And this brings us to the question as to whether in a piebald animal the pigmented hairs are in any way different from the pigmentless or white hairs. No adequate investigation of this subject has yet been made, but some observations made by the author of this article, on the piebald black and white rat, show that differences connected with the microscopic structure exist.
There is thus evidence that colour is correlated with other factors which determine pattern. And this leads to the inquiry as to whether albinoes ever exhibit evidence that they carry the pattern determinants in the absence of those for pigmentation. For it is to be expected a priori that, since albinoes were derived from pigmented progenitors and may at any time appear, side by side with pigmented brothers, in a litter from pigmented parents, they would be carrying the pattern determinants of some one or other of their pigmented ancestors. Now we know, from the numerous experiments in heredity which have resulted since the rediscovery of Mendel’s principles, that an individual may carry a character in one of two conditions. It may be carried as a somatic character, when it will be visible in the body tissues, or it may be carried as a gametic character, and its presence can only then be detected in subsequent generations, by adequately devised breeding tests.
With regard to pattern, the evidence is now clear that albinoes may carry the determinants in both these ways. So far as they are carried gametically, i.e. by the sex-cells, it has been shown by Cuénot and G. M. Allen for mice, by C. C. Hurst for rabbits, and by L. Doncaster and G. P. Mudge for rats, that in a cross between a coloured individual of known gametic purity and an albino, the individuals of the progeny in either the first or second, or both generations, may differ, and that the difference in some cases wholly depends upon the albino used. It has been shown that the individuals in such an offspring may bear patterns which never occurred in the ancestry of the coloured parent, but did in that of the albino; and, moreover, if the same coloured parent be mated with another individual, either albino or coloured, that their offspring may never contain members bearing such patterns. The particular pattern will only appear when the coloured parent is mated with the particular albino. And yet the albino itself shows no somatic pattern or pigment. So clear is the evidence on this point that any one adequately acquainted at first hand with the phenomena, by employing an albino of known gametic structure and mating it with a coloured individual, also of known gametic constitution, could predict the result.
With respect to albinoes carrying pattern as a visible somatic character, i.e. in the body cells, no definite evidence has as yet been published. But W. Haacke has described a single albino rat, in which he states that the hairs of the shoulder and mid-dorsal regions were of a different texture from those of the rest of the body. And it is possible that this albino, had it developed colour, would have been of the piebald pattern. But the author of this article has quite recently reared some albinoes in which the familiar shoulder hood and dorsal stripe of the piebald rat is perfectly obvious, in spite of the absence of the slightest pigmentation. The hairs which occupy the region which in the pigmented individual is black, are longer, thinner and more widely separated than those in the regions which are white. As a result of this, the pink skin is quite visible where these hairs occur, but elsewhere it is invisible. Thus these albinoes exhibit a pattern of pink skin similar in form with the black pattern of the piebald rat. Moreover, some of the albinoes possess these particular “pattern” hairs all over the body and obviously such individuals are carrying the self pattern. There are other details into which we cannot here enter, but which support the interpretation put upon these facts, i.e. that these particular albinoes are carrying in the soma the pattern determinants simultaneously with the absence of some of the factors for pigmentation.
Not only do albinoes thus carry the determinants for pattern, but it has been known for some time that they also carry gametically, but never visible somatically, the determinants for either the ferment or the chromogen for one or more colours. L. Cuénot was the first to show this for albino mice. He was able by appropriate experiments to demonstrate that when an albino is derived (extracted) from a coloured ancestry, and is then crossed with a coloured individual, both the colour of the pigmented parent and of the pigmented ancestry of the albino may appear among the individuals of the offspring.
Immediately subsequent to Cuénot, G. M. Allen in America demonstrated the same fact upon the same species of rodents. C. C. Hurst, more recently, has shown that albino rabbits. whether pure bred for eight generations at least, or extracted from pigmented parents, may carry the determinants for black or for black and grey. In this latter case the determinants for black are carried by separate gametes from those carrying grey, and the two kinds of sex-cells exist in approximately equal numbers. This is likewise true of albino mice when they carry the determinants for more than one colour.
Since Hurst’s work, L. Doncaster and G. P. Mudge have both shown that albino rats also carry in a latent condition the determinants for black or grey. The experiments of the latter author show that, if a gametically pure black rat be crossed with an albino derived from a piebald black and white ancestry, all the offspring in successive litters will be black; but if the same black parent be crossed with albinoes extracted from parents of which One or both are grey, then both grey and black members will appear in the successive litters.
The proportions in which the various coloured individuals appear are approximately those demanded by the Mendelian principle of gametic purity and segregation. Cuénot and Hurst have also shown that when albinoes of one colour extraction are crossed with albinoes of another colour extraction the segregation of the colour determinants in the gametogenesis of the albinoes takes place in precisely the same way that it does in the gametogenesis of a pigmented individual; that is, in Mendelian fashion. Or, to express it otherwise, an albino extracted from yellow parents, bred with an albino extracted from black parents, will give an albino offspring whose gametes in equal numbers are bearers of the black and yellow determinants. And when one of these albinoes is bred with a pure coloured individual, a mixed offspring will appear in the first generation. Some of the individuals will be one or other of the two colours, the determinants of which were borne by the albino, and others the colour of the pigmented parent. But in such albino crosses the colour characters are latent because albinoes do not carry the whole of the complements for colour production. They carry only some determinant or determinants which are capable of developing colour when they interact with some other determinant or determinants carried alone by pigmented individuals. Whether albinoes carry the tyrosinase or other ferment, or whether they carry the chromogen or chromogens, is not yet settled. Miss Durham’s work suggests that they carry the latter. But that they never bear both is proved by the fact that, when albinoes are crossed with each other, none but albinoes ever result in the offspring. One apparent exception to this rule only is known, and this almost certainly was due to error.
It is not only among albino animals that colour factors are carried in a latent condition, but also in white flowers. W. Bateson has shown this to be the case for the sweet-pea (Lathyrus odoratus), var. Emily Henderson, and for certain white and cream stocks (Matthiola). When white Emily Henderson (the race having round pollen grains) is crossed with a blue-flowered pea, purple offspring result. Similarly, when white Emily Henderson (long pollen grains) is crossed with white Emily Henderson (round pollen grains), the offspring wholly consists of the reversionary purple type, and sometimes wholly of a red bicolor form known as “Painted Lady.” These two types never appear in the same family. With the stocks, when a white-flowered and hairless form is crossed with a cream-flowered and hairless one, all the offspring are purple and hairy. Bateson considers that the purple colour is due to the simultaneous existence in the plant of two colour factors which may be designated by C and R. If either one of these two is absent the plant is colourless. Cream-coloured flowers are regarded as white because cream is due to yellow plastids and not to sap colour. Thus the cream plant may carry C and the white one R. When they are crossed the two factors for colour production are brought together. Obviously, we may regard C as a tyrosinase and R as a chromogen, or vice versa; and in the case of the white sweetpea crossed with a blue-flowered one, and producing purple offspring, we may imagine that the white flower brought in an additional tyrosinase or a chromogen not present in the blue flower, which, when combined or mixed with the chromogen or tyrosinase for blue, gave purple. A similar explanation may apply to C. Correns’s experiment, in which he crossed white Mirabilis jalapa with a yellow form, and always obtained red-flowered offspring.
In heredity, complete albinism among animals is always recessive; and partial albinism (piebald) is always recessive to complete pigmentation (self-coloured). When an albino mouse, rat, guinea-pig or rabbit is crossed with either a pure self or pure pied-coloured form, the offspring are similar to, though not always exactly like, the coloured parent; provided, of course, that the albino is pure and is not carrying some colour or pattern determinant which is dominant to that of the coloured parent used. No albinoes, in such a case, will appear among the first generation, but if the individuals of this (F.1) generation are crossed inter se or back crossed with the albino parent, then albino individuals reappear among the offspring. In the former case they would form one-quarter of the individuals of this second (F.2) generation, and in the latter, one-half.
The recessive nature of albinism and its distribution in Mendelian fashion is almost certainly as true for man as for lower forms. This has been shown by W. C. Farabee for negroes in Coahoma county, Mississippi. The facts are as follows. An albino negro married a normal negress. They had three children, all males. All three sons married, and two of them had only normal children, judged of course by somatic characters. But the third son married twice, and by the first wife had five normal and one albino children, and by the second, six normal and three albino children. If we assume that the two negresses which the third son married were themselves carrying albinism recessive—an exceedingly probable condition considering that albino negroes are not uncommon—the result is accurately in accordance, as W. E. Castle has shown, with Mendelian expectation. For there is expected in the offspring of this third son coloured individuals and albinoes in the proportion of 3:1. There is actually 11:4, which is the nearest possible approximation with the number 15.
The operation of Mendelian processes in human heredity is further shown by the close relationship that exists between the appearance of albinoes and cousin marriages. An albino is a homozygote; that is, all its gametes are carrying the character of albinism and none of them bear the alternative character—the allelomorph—of pigmentation. By pigmentation is here meant all those factors which go to its production. Now such a gametic (egg or sperm) constitution can only result when two individuals, all or some of whose gametes are pure with regard to the character albinism, meet in fertilization. Hence it is readily seen that it is among cousin marriages that the greater probabilities exist that two individuals bearing identical characters will meet, than in the population at large. This can be illustrated in the following scheme. Let A stand for a pure albino and (A)N for a normal person, who nevertheless carries the character albinism (A) recessive. Then, in the scheme below, if Ab and (A)Nb are two brothers who both marry normal wives N, their children N(A) in the first case will be all normal in appearance but will be carrying albinism recessive; and in the second case some will be pure normal individuals N, and some will be like the children of the first brother, i.e. N(A). Now, if one of these latter children of the second brother marries a cousin—a child of the first brother,—their offspring, if large enough, will consist of some pure normals N, impure normals N(A), and of albinoes A.
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No other rational explanation of the close relationship between albinism and cousin marriages is at present forthcoming. And, when the whole facts are borne in mind, there can be no reasonable doubt that the Mendelian principles offer an intelligible solution of the problem.
A popular conception exists that albinoes are less constitutionally strong than the pigmented individuals of the same species. In support of this belief there is more or less scientifically ascertained evidence. Conversely, there is, however, conclusive evidence that in some instances and in respect of certain qualities the opposite belief is true.
To deal with the former belief first, we have the remarkable case cited by Charles Darwin on the authority of Professor I. J. Wyman. In Virginia the paint-root plant (Lachnanthes tinctoria) occurs abundantly, and Professor Wyman noticed that all the pigs in this district were black. Upon inquiry of the farmers he found that all the white pigs born in a litter were destroyed, because they could not be reared to maturity. The root of this plant, when eaten by white pigs, caused their bones to turn to a pink colour and their hoofs to fall off, but the black pigs could eat the same plant with impunity. Partial albinism in this case was undoubtedly correlated with some inherent constitutional defect, in virtue of which the individuals characterized by it were injuriously affected by the juices of a plant quite innocuous to their pigmented brethren. Heusinger has shown that white sheep and pigs are injured by the ingestion of certain plants, while the pigmented individuals may eat them without harm. In Devonshire and in parts of Kent the farmers entertain a marked prejudice against white pigs, because “the sun blisters their skin.” More remarkable is the case of certain cattle, whose skin is piebald, marked by a general ground colour over which are scattered patches of unpigmented coat. In these animals, in certain inflammatory skin eruptions, caused by the ingestion of harmful plants, the albinotic areas are alone affected. And with certain cutaneous diseases accompanied by constitutional disturbances which afflict cattle, the affection in the skin appears on the patches bearing white hairs, the other parts remaining apparently healthy. Such cases suggest that we should be more correct in regarding, not albinism as correlated with constitutional defects, but rather pigmentation as correlated with powers of immunity or increased resistance against certain injurious processes. In the West Indies “the only horned cattle fit for work are those which have a good deal of black in them; the white are terribly tormented by the insects and they are weak and sluggish in proportion to the black.”
Coming to man, it is known that some albino negroes are peculiarly sensitive to the bites of insects; and with Europeans it is a generally observed fact that the fairer individuals are more seriously affected by the bites of fleas and bugs than are darker ones. Dr Twining, in the British Association Reports for 1845, p. 79, cites some instances described by Humboldt, who says that the copper-coloured natives of the high plain of Bogoto, and at a lower level on the Magdalena river, were generally free from goitre. Professor Poffig, also cited by Dr Twining, states that on the east side of the Andes in Chile, in some of the races which live there, he did not see a single case of goitre, and yet in the white inhabitants, who live exactly as the natives, it prevails in a great degree:
Turning now to instances of the opposite kind, it is known that silkworms which spin colourless cocoons are more resistant to the attacks of a certain deadly fungus than are those which spin the yellow ones. In some parts of North America it is found that the white peaches are much less liable to the attack of a disease known as the “yellows” than are the yellow-fleshed ones. In the region of the Mississippi, Farabee has observed that the albino negroes are taller and broader than the black-skinned individuals. We may assume that increased stature and breadth imply some sort of inherent physical superiority, and if such an assumption is valid we have in man evidence that albinism is correlated not with constitutional defectiveness but with greater perfectness.
But the question as to whether albinoes are more or less constitutionally vigorous than pigmented individuals of the same species may be tested by exact measurement. In 1893 W. D. Halliburton and T. G. Brodie, in ascertaining the physiological properties of nucleo-proteids, found that when they were intravascularly injected into pigmented rabbits, coagulation of the blood resulted, but of the eight albinoes which they used, none clotted. At a subsequent period (1897) Halliburton and J. W. Pickering showed that the three synthesized colloids of Grimaux in the same way produced coagulation in pigmented animals, but failed to do so in albinoes. Pickering, still later, showed, in the case of four Norway hares, two of which were injected while in their pigmented or summer coat, and two while in their albino or winter coat, that coagulation occurred in the former cases but not in the latter.
Quite recently, however, the author of this article has made a more detailed examination of the question, operating upon several hundreds of rabbits. And he found that all albinoes do not fail to clot when intravascularly injected with nucleo-proteids. Only about 9% of them thus failed absolutely to manifest any trace of coagulation. But about 7% showed an exceedingly limited coagulation, in which the clot was colourless and flocculent, and confined to the heart. The rest gave a typical and more or less wide-spread coagulation. Moreover, it was found that all the failures of coagulation occurred when the nucleo-proteid used was obtained from pigmented animals. When it was derived from albinoes no failures occurred. All pigmented animals clotted when the nucleo-proteid was derived from either source. The Himalayan rabbits reacted like complete albinoes, and 12% of them failed to clot when injected with nucleo-proteid extracted from pigmented animals.
The interesting fact was thus ascertained that all albinoes are not alike. To students of heredity this is precisely what would have been expected. For, as the facts above described show, albinoes, though apparently identical externally, are yet the carriers of different hereditary characters. Among albino rats, for instance, the author of this article has reason to believe, upon theoretical grounds resting on an experimental basis, that probably no less than thirteen types exist. With rabbits and mice there must be a still larger number.
In the intravascular coagulation experiments above described, all the rabbits were carefully weighed, and the amount of nucleo-proteid injected until coagulation occurred was measured. This would give for albinoes and pigmented individuals the amount per kilogramme of body-weight required to kill in each case, and would afford a measurement of the relative resistance of the two races. It was found that the resistance of albinoes towards the coagulative effects of injected nucleo-proteids was to that of pigmented individuals as 1·5 to 1·0. In this case, the greater constitutional vigour of the albino is thus accurately demonstrated. But it does not necessarily follow that with other materials and with other constitutional qualities the state of things would not be reversed.
One other feature remains to be mentioned. Albinism appears, in the processes of heredity, to be sometimes indissolubly correlated with certain peculiar traits. It is well known that the long-haired albino rabbit, called Angora, when at rest, has the habit of swaying its head sideways in a peculiar fashion. C. C. Hurst has shown that the long-haired and albino characters are always accompanied in heredity with the swaying habit. The Angora character never occurs without it.
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