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their mode of formation. Although the formation of toxins with characteristic action can be demonstrated by these two methods, it must not be inferred that this can be done in every instance. On the contrary, it is highly methods used in pharmacology. In other instances the probable that some toxins are only produced in the living toxins are retained to a large extent within^ the bacteria, tissues. We have at least examples of intense local toxic and in this case the dead bacteria are injected as a action round living bacteria, which have not yet been reprosuspension in fluid. Sometimes, as in the preparation of duced by means of separated toxins. Not only are the Koch’s new tuberculin, the bacteria are bruised in _ an general symptoms of poisoning in bacterial disease due to agate mortar, so as to set free the intracellular toxins. toxic substances, but also the tissue changes, many of them The bacteria are usually killed by chloroform vapour or of inflammatory nature, in the neighbourhood of the bacteria. to mention examples, diphtheria toxin produces insome volatile antiseptic, the agent used being afterwards Thus, flammatory oedema which may be followed by necrosis; got rid of by evaporation; when the toxins are comparatubercle bacilli give rise to a tubercle-like nodule, Arc. tively resistant to heat, a suitable temperature may be dead Furthermore a bacillus may give rise to more than one used for the purpose. The study of the nature of toxins requires of course the various methods of organic toxic body, either as stages in one process of change or chemistry. Attempts to obtain them in an absolutely as distinct products. Thus paralysis following diphtheria pure condition have, however, failed in important cases. is in all probability due to a particular modification of the ordinary toxin, sometimes formed in specially large So that when a “ toxin ” is spoken of, a mixture with amount. . . other organic substances is usually implied. Or the Regarding the chemical nature of toxins less is known toxin may be precipitated with other organic substances, than regarding their physiological action. Though an purified to a certain extent by re-solution, re-precipitation, enormous amount of work has been done on of &c., and desiccated. A “dry toxin” is thus obtained, the subject, no important bacterial toxin has as Nature toxins. though still in an impure condition. Toxic substances yet been obtained in a pure condition, and,, have also been separated by corresponding methods from though many of them are probably of proteid nature, the bodies of those who have died of certain diseases, and even this cannot be asserted with absolute certainty. the action of such substances on animals is in some cases Brieger, in his earlier work, found that, alkaloids were an important point in the pathology of the disease. formed by bacteria in a variety of conditions, and that Another auxiliary method has been applied in this de- some of them were poisonous. These alkaloids he called partment, viz., the separation of organic substances by ptomaines. The methods used in the investigations were, filtration under high pressure through a colloid membrane, however, open to objection, and it is. now recognized that gelatine supported in the pores of a porcelain filter being although organic bases may sometimes be formed, an usually employed. It has been found, for example, that may be toxic, the important toxins are not of that nature. a toxin may pass through such a filter while an antitoxin A later research by Brieger along with Fraenkel pointed may not. The methods of producing immunity will be to the extracellular toxins of diphtheria, tetanus, and described in connexion with that subject. . other diseases being of proteid nature, and various The fact that in anthrax, one of the first diseases to be other observers have arrived at a like conclusion, i e fully studied, numerous bacilli are present in the blood of general result of such research has been to show that the infected animals, gave origin to the idea that Bacteria tpe organisms might produce their effect by toxic bodies are, like proteids, precipitable by alcohol and as a ents J using ^up^ the oxygen of theiteblood. Such various salts; they are soluble in water, are somewhat Off disease. _ a subsidiary knQWn to be qu easily dialysable, and are relatively unstable both to light and heat. Attempts to get a pure toxin by repeated matter. And although effects may sometimes be pro- precipitation and solution have resulted in the producduced in a mechanical manner by bacteria plugging tion of a whitish amorphous powder with highly toxic capillaries of important organs, e.g., brain and kidneys, properties. Such a powder gives a proteid reaction, and it may now be stated as an accepted fact that ail the is no doubt largely composed of albumoses, hence the important results of bacteria in the tissues are due to toxalbumoses has been applied. . The question has, poisonous bodies or toxins formed by them. Here, just name however, been raised whether the toxin is really itself a as in the general subject of fermentation, we must inquire proteid or whether it is not merely carried down with the whether the bacteria form the substances in question precipitate. Recently Brieger and Boer, have by predirectly or by means of non-living ferments or enzymes cipitation with certain salts, notably of zinc, obtained a With regard to toxin formation the following general body which is toxic but gives no reaction of any form of statements may be made. In certain instances, e.g., m proteid There is of course the possibility that the toxin the case of the tetanus and diphtheria bacilli, the pro- is a proteid, but is in so small amount that it escapes duction of soluble toxins can be readily demonstrated by detection. These facts show the great difficulty of the filtering a culture in bouillon germ-free by means of a problem, which is probably insoluble by present methods porcelain filter, and then injecting some oi the filtrate of analysis; the only test, in fact, for the existence of into an animal. In this way the characteristic features of a toxin is its physiological effect. It may also be menthe disease can be reproduced. Such toxins being set tioned that many toxins have now been obtained by free in the culture medium are often known as extra- crowing the particular organism in a proteid-free medium, cellular. In many cases, however, the filtrate, when a fact which shows that if the toxin is a proteid it may be iniected, produces comparatively little effect, whilst toxic formed synthetically by the bacterium as well as by action is observed when the bacteria in a dead con- modification of proteid already present. With regard to dition are used; this is the case with the organisms the nature of intracellular toxins, there is even greater of tubercle, cholera, typhoid, and many others. Ihe difficulty in the investigation and still less is known. toxins are here manifestly contained within the bodies Many of them, probably also of proteid nature, are much of the bacteria, i.e., are intracellular, though t ey more resistant to heat; thus the intracellular toxins of may become free on disintegration of the bacteria. The the tubercle bacillus Retain certain of their effects even distinction between the two varieties, though convenient, after exposure to 100° C. must not be pushed too far, as we know little regarding

sufficiently small to retain them. The passage of the fluid is readily effected by negative pressure Separation pr0(juce(j aii ordinary water exhaust-pump. of toxins. rpjie eg-ccts 0f the filtrate are then tested by the