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The Principles of General Prophylaxis.

The principle of rational prophylaxis and combative efforts against all infec- tious diseases consists in measures directed against the causal agents of these diseases. Such measures as are to be of value in eradicating a disease like plague, have to be directed straight to the root of the evil, namely, to the destruction of its causal agent-the now well known Bacillus pestis. Without a knowledge of the agent at work in the production of the disease, our efforts at a rational pro- phylaxis would fall far short of the necessary standard.

Bound up closely with this knowledge of the specific causative agent, are other factors which are of importance, namely, a knowle lze of the biological cha- racteristics of the micro-organism, of the powers possessed by the organism to produce the disease, of the question of immunity, and of the necessary conditious of life for the maintenance of the bacillus inside and outside the body.

A knowledge of the morphological characters of the plague bacillus is of the highest importance in a general sense, especially for purposes of diagnosis and an early recognition of the disease, but so far as prophylactic measures are concerned, these characteristics are of relatively little importance.

In order that such an organisin as the Bacillus pestis may produce the symp- tom-complex of plague, certain conditions must be present. In the first place, there must be a source of infection producing the bacillus and supplying it in a living and virulent condition. Without such it is inconceivable for the disease to break out. Epidemiology has established the fact, that exotics as plague which are not endemic in a country, never have an autochthonus origin, but are always introduced from without. The most important source of infection is of course an individual suffering from the disease, and more particularly the secretions and excretions from his body. Again, so called latent cases are of importance, in which the individual appears in good health, yet harbours enormous numbers of the specific germs and scatters them about him. This sort of thing is well known in the case of cholera and would appear to hold good for plague (vide cases of accidental death in which the B. pestis has been found in the blood and internal organs).

Again, a source of infection and one of the highest importance so far as plague is concerned, is the occurrence of the disease in animals. Rats suffering from plague, constitute probably the most important element of danger to man. These vermin are known to harbour plague bacilli for long periods of time. The disease is often chronic in them, and the occurrence of latency in rat plague cannot be dis- regarded in the light of the most modern research. Again, other anima's, as cats, fowls, calves, sheep, pigs, etc., are susceptible to plague infection, and become thereby elements of danger to the general public who frequently come into close contact with them.

The question as to the importance of water, soil. air, etc., in regard to the spread of plague may be discarded to a great extent. The danger attached to these elements would appear to have been grossly over-estimated. Food as a source of the disease has abready been dwelt upon under a separate heading. The conta- mination of food by veruin, insects. the handling by infectel persons of articles, etc., is a subject requiring the most earnest consideration on the part of Sanitary authorities. My own researches appear to show that plague to a great extent is a disease originating in the alimentary canal, the conveyance of the infection being effected through plague infected articles of diet.

The avenues of infection in plague may be divided into direct and indirect ways. Direct infection is mainly occasioned through wounds and direct inocula- This mode would not appear to play an important part in the spread of the

tion. disease.

Indirect infection, on the other hand, is of the highest importance. The presence of innumerable plague infected rats, scattering broadcast hoards of plague bacillus through their secretions and excretions, rendering possible the gross infection of food, water, etc., constitutes an element of great danger to public health. Again the clothing and linen of plague patients may be the means of conveying the infection to the extreme ends of the earth.