exerts this action upon the bacteria. The opsonic index is obtained
by comparing the average number of bacilli taken up by, say,
100 leukocytes, to which the serum from a tuberculous patient
has been added, with the number of bacteria taken up by ajhundred
similar corpuscles to which normal serum has been added, the
ratio between the two giving the opsonic index. Wright maintains
that after the injection of small doses of tuberculin during
a negative phase which first appears, i.e. whilst there is a fall in
the number of bacilli taken up by the leukocytes of the blood, the
patient is more susceptible than before to the attacks of the tubercle
bacillus. Following this, however, there is a gradual rise in the
opsonic index until it passes the normal and the patient enters
a positive phase, during which the susceptibility to the attacks
of the tubercle bacillus is considerably diminished. When the
effects of this dose are passing off a fresh injection should be made;
this again induces a negative phase, but one that should not be so
marked as in the first instance, whilst the positive phase which
succeeds should be still more marked than that first obtained. If
this can be repeated systematically and regularly the patient
should begin, and continue, to improve. The difficulties involved
in the determination of the opsonic index are, however, exceedingly
great, and the personal factor enters so largely into the question
that some observers are very doubtful as to the practical utility
of this method. In Wright's hands, however, and in the hands of
those who work with him, very satisfactory results are obtained.
The tuberculin treatment, fortunately, does not stand or fall by
the success of the opsonic index determination, especially as most
valuable information as to the course of the disease and the effects
of the tuberculin may be obtained by a study of the daily temperature
chart and of the general condition of the patient.
Tuberculin should not be injected more frequently than about once in 10 or 14 days, and it is well not to increase the dose too rapidly. Wherever the temperature continues high, even a degree beyond normal, and where the pulse is over 100, it is not wise to give tuberculin, nor does it seem to be of any great value where the disease is making rapid headway or has become generalized, especially where there is meningitis or bleeding from the lungs.
It is interesting to note, in connexion with the diagnostic significance of the opsonic index, that in non-tuberculous subjects the administration of a small dose of tuberculin is followed by no negative phase such as is met with in the tuberculous subject. The phagocytic power of the white blood corpuscles is determined by noting the number of organisms taken up by the leukocytes when mixed with equal parts of a standard emulsion of tubercle bacilli and blood serum incubated in fine glass tubes for 15 minutes at a temperature of 37° C. If the period of incubation is much shorter than this the results are irregular, whilst if the period is longer so many organisms are taken up that it becomes impossible to differentiate two sets of sera.
As an example we might adduce the following. Taking a tuberculous patient's serum + leukocytes + tubercle bacilli, let us say we have an average of i-S bacilli per leukocyte in 50 or 100 leukocytes counted; with normal serum -f- corpuscles -t- tubercle bacilli the average number of bacilli per leukocyte in the same number of cells counted is 3. From these figures the opsonic index obtained is 1-8 -j- 3 = 0-6 = opsonic index.
Leprosy. — Armauer Hansen in 1871, and Neisser in 1881, described a " leprosy bacillus " corresponding in size and in certain points of staining reaction to the tubercle bacillus, and it is now generally accepted that this bacillus is the direct and specific causal agent of leprosy. The discovery of this organism paved the way for the proof that the tubercular and anaesthetic forms of leprosy are essentially the same disease, or rather are the manifestations of the action of a common organism attacking different series of tissues.
To demonstrate the presence of the leprosy bacillus, tie an indiarubber ring firmly around the base of one of the leprosy tubercles. As soon as the blood is driven out, leaving the nodule pale, make a puncture with the point of a sharp knife. From this puncture a clear fluid exudes; this, dried on a cover glass, stained with carbol-fuchsin, and rapidly decolonized with a weak mineral acid, shows bacilli stained red and very like tubercle bacilli; they differ from that organism, however, in that they are somewhat shorter, and that if the acid be too strong or be allowed to act on them for too long a time, the colour is discharged from them much more readily. These organisms, which are from 4 to 6/i in length and o-^n in breadth, are as a rule more rigid and more pointed than are the tubercle bacilli (see Plate II., fig. 16). It is doubtful whether they form spores. They are found in large numbers lying embedded in a kind of gelatinous substance in the lymphatics of the skin, in certain cells of which they appear to be taken up.
It is curious that these bacilli affect specially the skin and
nerves, but rarely the lungs and serous membranes, thus being in sharp contrast to the tubercle bacillus, which affects the latter very frequently and the former more rarely. They are seldom found in the blood, though they have been described as occuring there in the later stages of the disease. It is stated that leprosy has been inoculated directly into the human subject, the patient dying some five or six years after inoculation; but up to the present no pure culture of the leprosy bacillus has been obtained; it has therefore been impossible to produce the disease by the inoculation of the bacillus only. What evidence we have at our disposal, however, is all in favour of the transmissibility of the disease from patient to patient and through the agency of the leprosy bacillus. None of the numerous non-bacillary theories of leprosy account at all satisfactorily for this transmissibility of the disease, for its progressive nature, and for the peculiar series of histological changes that are met with in various parts and organs of the leprous body. Leprosy occurs in all climates. It is found where no fish diet can be obtained, and where pork and rice are never used, though to these substances has been assigned the power of giving rise to the disease. Locality appears to influence it but little, and with improved sanitation and increased cleanliness it is being graduaUy eradicated. The only factor that is common in all forms of leprosy, and is met with in every case, is the specific baciflus; and in spite of the fact that it has yet been found impossible to trace the method of transmission, we must from what is known of the presence and action of bacilli, in other diseases, especially in tuberculosis, assign to the leprosy bacillus the role of leprosy-producer, until much stronger evidence than has yet been obtained can be brought forward in favour of any of the numerous other causes that have been assigned. Two cases are recorded in which people have contracted leprosy from pricking their fingers with needles whilst sewing a leper's clothes; and a man who had never been out of Dublin is said to have contracted the disease by sleeping with his brother, a soldier who had returned from India suffering from leprosy.
Glanders. — Farcy in the human subject resembles the same disease experimentally produced in animals with material from a slandered animal, and as there is no pathological distinction between the two, from the etiological standpoint, they may be considered together. If the pus from a glanders abscess be mixed with a little sterile saline solution and spread over the cut surface of a boiled potato kept at the body-temperature, bright yellow or honey-coloured, thick, moist-looking colonies grow very rapidly and luxuriantly. These colonies gradually become darker in colour, until they assume a cafe-au-lait, or even a chocolate, tint. On examining one of them microscopically, it is found to be made up of bacilli 2 to 5/x long and 1 to |- of their own length broad (see Plate I., fig. 2 and fig. 6). The bacillus is usually straight or slightly curved and rounded at one end; it appears to be non-motile. As first pointed out by Loeffler and Schiitz, when a portion of a culture is inoculated subcutaneously, typical farcy, with the acute septicaemia or blood-poisoning so characteristic of certain cases of glanders and farcy, is the result. The human subject is usually inoculated through wounds or scratches, or through the application of the nasal discharge of a slandered animal to the mucous membrane of the nose or mouth. Man is not specially susceptible to the glanders virus, but as he frequently comes into contact with slandered horses a considerable number of cases of farcy in man are met with, although amongst knackers it is a comparatively rare disease. Cattle never contract it by the ordinary channels, and even when inoculated exhibit nothing more than localized ulceration. The goat appears to occupy an intermediate position between cattle and the horse in this respect; in sheep, which are fairly susceptible the disease runs its course slowly, and appears to resemble chronic farcy in man. In rabbits and the dog the disease runs a very slow and modified course. Although field-mice are extraordinarily susceptible, white mice and house mice, unless previously fed on sugar or with phloridzin, are unaffected by inoculation of the glanders bacillus. The pigeon is the only bird in which glanders has been produced. Lions and tigers are said to contract the disease, and to take it in a very severe and
