Page:EB1911 - Volume 20.djvu/841

Rh pure culture. Distinct colonies may often be found as early as the eighth or twelfth hour of incubation; in from eighteen to Lvventy-four hours they appear as rounded, elevated, moderately translucent, greyish white colonies, with a yellow tinge, the surface moist and the margins slightly irregular or scalloped. They are thicker and somewhat more opaque in the centre. When the colonies are few and widely separated, each may grow to a considerable size, 4 to 5 mm.; but when more numerous and closer together, they remain small and almost invariably discrete, with distinct intervals between them. In older growths the central opacity becomes more marked and the c renal ion more distinct, the moist, shiny appearance being lost. When the surface of the serum is dry, the growth, as a rule, does not attain any very large size.

These " pure " colonies, when sown in slightly alkaline broth, grow with great vigour; and if a small amount of such a 48 hours' culture be injected under the skin of a guinea-pig, the animal succumbs, with a marked local reaction and distinct symptoms of to.xic poisoning very similar to those met with in cases of diphtheria of thehumansubject. Roux and Yersin demonstrated that the poison was not contained in the bodies of the bacilli, but that it was formed and thrown out by them from and into the nutrient medium. Moreover, they could produce all the toxic symptoms, the local reactions, and even the paralysis which often follows the disease in the human subject, by injecting the culture from which they had previously removed the whole of the diphtheria bacilli by filtration. This cultivation, then, contains a poisonous material, which, incapable of multiplying in the tissues, may be given in carefully graduated doses. If, therefore, there is anything in the theory that tissues may be gradually "acclimatized" to the poisons of these toxic substances, they saw that it should be possible to prove it in connexion with this disease. Behring, going still further, found that the tissues so acclimatized have the power of producing a substance capable of neutralizing the toxin, a substance which, at first confined to the cells, when formed in large quantities overflows into the fluids of the blood, with which it is distributed throughout the body. The bulk of this toxin-neutralizing substance remains in the blood-serum after separation of the clot. In proof of this he showed that (1) if this serum be injected into an animal before it is inoculated with even more than a lethal dose of the diphtheria bacillus or its products, the animal remams perfectly well; (2) a certain quantity of this serum, mixed with diphtheria toxin and injected into a guinea-pig, gives rise to no ill effects; and (3) that even when injected some hours after the bacillus or its toxins, the serum is still capable of neutralizing the action of these substances. In these experiments we have the germ of the present anti toxic treatment which has so materially diminished the percentage mortality in diphtheria. This serum may also be used as a prophylactic agent.

The anti toxic serum as now used is prepared by injecting into the subcutaneous tissues of a horse the products of the diphtheria bacillus. The bacillus, grown in broth containing peptone and blood-serum or blood-plasma, is filtered and heated to a temperature of 68° or 70° C. for one hour. It then contains only a small amount of active toxin, but injected into the horse it renders that animal highly insusceptible to the action of strong diphtheria toxins, and even induces the production of a considerable amount of antitoxin. This production of antito.xin, however, may be accelerated by subsequent repeated injections, with increasing doses of strong diphtheria toxin, which may be so powerful that | to J of a drop, or even less, is a fatal dose for a medium-sized guinea-pig. The anti toxic serum so prepared may contain 200, 400, 600 or even more " units " of antitoxin per c.c. — the unit being that quantity of antitoxin that will so far neutralize 100 lethal doses (a lethal dose is the smallest quantity that will kill a 250-gramme guinea-pig on the fifth day) of toxin for a 250-gramme gumea-pig, that the animal continues alive on the fifth day from the injection. This, however, is a purely arbitrary standard of neutralizing power, as it is found that, owing to the complicated structure of the toxin, the neutralizing and the lethal powers do not always go hand in hand; but as the toxin used in testing the antitoxin is always compared with the original standard, accurate results are easily obtained.

Diphtheria, though still prevalent in cities, has now lost many of its terrors. In the large hospitals under the Metropolitan

Asylums Board the death-rate fell from nearly 40% in 1889 to under 10% in 1003; and if antitoxin be given as soon as the disease manifests itself, the mortality is brought down to a very insignificant figure. It has been maintained that as soon as antitoxin came into use the number of cases of paralysis increased rather than diminished. This may be readily understood when it is borne in mind that many patients recover under the use of antitoxin who would undoubtedly have succumbed in the pre-antitoxin days; and it cannot be too strongly insisted that although the antitoxin introduced neutralizes the free toxin and prevents its further action on the tissues, it cannot entirely neutralize that which is already acting on the cells, nor can it make good damage already done before it is injected. Even allowing that antitoxin is not accountable for the whole of the improvement in the percentage mortality statistics since 1896, it has undoubtedly accounted for a very large proportion of recoveries. Antitoxin often cuts short functional albuminuria, but it cannot repair damage already done to the renal epithelium before the antitoxin was given. The clinical evidence of the value of antitoxin in the relief that it affords to the patient is even more important than that derived from the consideration of statistics.

The diphtheria bacillus or its poison acts locally as a caustic and irritant, and generally or constitutionally as a protoplasmic poison, the most evident lesions produced by it being degeneration of nerves and muscles, and, in acute cases, changes in the walls of the blood vessels. Other organisms, streptococci or staphylococci, when present, may undoubtedly increase the mortality by producing secondary complications, which end in suppuration. Diphtheria bacilli may also be found in pus, as in the discharges from cases of otorrhoea.

Tetanus {Lockjaw). — Although tetanus was one of the later diseases to which a definite micro-organismal origin could be assigned, it has long been looked upon as a disease typical of the "septic" group. In 1885 Nicolaier described an organism multiplying outside the body and capable of setting up tetanus, but this was only obtained in pure culture by Kitasato, a Japanese, and by the Italians in 1889. It has a very characteristic series of appearances at different stages of its development. First it grows as long, very slender threads, which rapidly break up into shorter sections from 4 tos^u in length (see Plate II. fig. 11). In these shorter rods spores may appear on the second or up to the seventh day, according to the temperature at which the growth occurs. The rods then assume a very characteristic pin or drumstick form; they are non-motile, are somewhat rounded at the ends, and at one end the spore, which is of greater diameter than the rod, causes a very considerable expansion. Before sporulation the organisms are distinctly motile, occurring in rods of different lengths, in most cases surrounded by bundles of beautiful flagella, which at a later stage are thrown off, the presence of flagella corresponding very closely with the " motile " period. The bacillus grows best at the temperature' of the body; it becomes inactive at 14° C. at the one extreme, and at from 42° to 43° C. at the other; in the latter case involution forms, clubs and branching and degenerated forms, often make their appearance. It is killed by exposure for an hour to a temperature of from 60° to 65° C; the spores however are very resistant to the action of heat, as they withstand the temperature of boiling water for several minutes. The organism has been found in garden earth, in the excrement of animals — horses — and in dust taken from the streets or from living-rooms, especially when it has been allowed to remain at rest for a considerable period. It has also been demonstrated in, and separated from the pus of wounds (see Plate II. fig. 12) in patients suffering from lockjaw, though it is then invariably found associated with the micro-organisms that give rise to suppuration.

It is important to remember that this bacillus is a strict anaerobe, and can only grow when free oxygen has been removed from the cultivation medium. It may be cultivated in gelatine to which has been added from 2 to 3 % of grape-sugar, when, along the line of the stab culture, it forms a delicate growth, almost like a fir-tree, the tip of which never comes quite to the surface of the gelatine. The most luxuriant growth — evidenced by the longest branches — occurs in the depth of the gelatine away from free oxygen. After a time the