THE VETERINARIAN.

New Zealand Mail, Issue 867, 12 October 1888, Page 18

THE VETERINARIAN.

Micro-Organisms. THEIR OFFICE IN NATURE. At the Royal Veterinary College, on Wednesday, June 20, Professor E. Crookshank, of King's College, gave a lecture to the advanced students on the subject of MicroOrganisms, or, as they are commonly termed, bacteria, in special reference to their effects on the higher living beiugs which they infest. The lecturer began by expressing his sense of the honour which he considered had been conferred ou him when the Principal of the college invited him to address the class on tho special subject to which he had devoted his attention for many years ; and he ventured to express a hope that the time is not far distant when every veterinary college will beprovided with a laboratory in which bacteriology may be taught systematically ou the modern method. Bacteria are miuute beings which stand in the borderland between the animal and plant worlds ; but, by consent, they are classed as plauts, because they can get their nitrogen from ammonia, which animals canuot do.

Various forms of bacteria aro recognised, and it is noticeable that the forms often vary, according to the circumstances under which they are placed. But there are certain tolei’ably constant and typical forms, which admit of a fairly satisfactory method of classification being adopted. First, the most simple organism is the coccus, a minute circular body, composed, as all bacteria a o, of an envelope enclosing protoplasmic contents. These cocci are subject to partial fission, which produces a double circle (diplo-cocci), or a packet of four (tetracocci), or of eight (sarcinococei), or they may form masses (staphylococci), or assume the chain-like character (streptococci). Next to thecircular form of micro-organism there is the rod or bacillus, and among these bodies are found a great variety of modifications of outline aud differences ol function. Soma of them aro oval and do not form spores ; others are elongated and multiply by spores ; others assume a spiral form ; and some are turned back upon themselves, forming a double spiral. Referring to the functions of bacteria, the lecturer explained that they are in most cases quite definite and characteristic, and naturally place the organisms in several distinct groups. One group includes all bacteria which produce colours ; for example, the Micrococcus prodigiosus, which causes the body in which it grows to assume a blood tint. This organism, has the peculiar property of multiplying rapidly and suddenly without any apparent cause, and has from time to time, by its sudden appearance in water or in bread, caused considerable alarm in the minds of the people in districts where it lias shown itself unexpectedly. Another group includes all micro-organisms which possess the power to set up the process of fermentation. A third group contains all putrefactive organisms ; and in the fourth group are the most interesting and important microbes which are concerned in the causation of disease.

In the disease-causing group are found all the forms which have been described, and it is therefore impossible to determine by tho examination of the organism, oven by the aid of the best microscope, what is its function. This is to be settled only by prolonged observation and experiment.

In air, earth, water, and also in living beings, multitudes of micro-organisms are found ; aud in order to demonstrate that any one of them belongs to the disease-producing group, it is necessary that the following conditions be fulfilled.

First, the organism must always bo found in the diseased animal, either in the blood or the tissues, or in both. Next, the organism must be cultivated quite pure, that is, separate from other organisms, for several generations. Thirdly, the pure cultivation, when introduced into the system of a suscep* tible animal, must induce tho same disease j and further it is necessary that the organism should be recoverable from the blood or tihsues, or both, of the inoculated animal. When all these conditions are maintained—as they are, for example, in regard to the organism of anthrax—it may be affirmed with oertainty that the organism has a direct influence in causing the disease with which it is always associated. But the mere fact of a particular o-ganism being found in a particular disease is only one step in the inquiry, which must be followed to its completion before any conclusion can be drawn from the evidence.

In the attempts which have been made to explain tho mode of action of bacteria in tho production of disease, three different theories have been formulated by different observers ; neither of them, however, satisfactorily explains the phenomena which occur. One theory ascribes the injuiious effects of the disease-producing microbes to the interruption of the circulation, owing to the blocking up of the capillaries by the rapid accumulation of tho organisms. This condition may be seen in some preparations of organs of animals which have died of anthrax ; but it is quite certain that it is not constant, nor is it general iu the system of the diseased animal, and it cannot, therefore, bo referred

to in explanation of tlie fatality, which is invariable.

Two other modes of explanation are given, and each is more reasonable than the mechanical one just referred to. It is known that bacteria act on the animal tissues in such a manner that they supply themselve with material for their own support therefrom ; in fact, they feed on the higher organisms. It may, however, be proved that the mere consumption of some of tho nutritive parts of animals by the micro-organism is quite insufficient to explain the rapid destruction of life which follows from inooulation with anthrax baoilli or those of mouse septicaemia, Tho final theory is tho most satisfactory, and it may be taken in connection with the one last noticed to account for the death of the infected animal by blood-poisoning. There is good evidence that bacteria, in effecting the. changes in the fluids aud solids of tho higher organisms which they invade, oauso the formation of poisonous alkaloids or ptomaines, which act on the system with considerable energy. It is therefore, as Professor Crookshank remarked at the conclusion of the lecture, not by what they remove in the form of food for themselves, but by what they leave behind in the form of poisonous compounds, that they set up disease in the system of their host.