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The plague bacillus would appear to be a most variable organism in this res- pect. In has been my experience, as well as that of others, that certain strains of the organism maintain their virulence for a long time; others, however, lose this power in a few days.
The reasons for such on occurrence are not clear. Probably the circumstance depends upon the culture mediuni, its alkalinity or acidity, or upon the establish- ment of some standard in regard to nutrient media, as recommended by EYRE, would, I think, obviate many of the indefinite conclusions at present arrived at.
The long life of the B. pestis does not obtain in nature. Here inany deleteri- ous factors are present. The presence of saprophytes, coupled with the action of heat, cold, chemical and mechanical influences prevent the organism propagating its spe- cies for many generations. This fact is of great importance from an epidemiolo- gical standpoint. It shows us that the specific germ of plague is unable to spread over a large area without the assistance of either the body of man or the tissues of animals. Again, the limitation of the life of the B. pestis as a saprophyte. convin- ces us that, for the dissemination of the disease, infected human beings and animals, e.g., rats, are the chief factors at work.
WILLIAM HUNTER.
The Avenues of Infection in Plague.
Since the days of the ancients who classified the ways of infection under three headings, namely, contactu, ad distans, and fomité, much has been added to our knowledge in regard to the habits of micro-organisms-pathogenic to man. The life history of these organisms, their biology, and significance in nature have been dealt with fully by many investigators.
The portals through which such organisins gain an entrance into the tissue of man and animals, still remains, so far as many infectious diseases are concerned, a dark chapter. Despite the efforts made by epidemiologists and others to unravel the mysteries of infection, much controversy still exists as to the particular channels availed of by different micro-organisms in order to reach the tissues of
man.
The avenues of infection are many. I propose to consider each of them separately and endeavour to show how many of them are of importance in the dissemination of plague.
Amongst the Chinese, certain ideas are widely prevalent as to the propagation of the disease. They attach great importance to infected food. They believe that diseased chickens cause plague. Again reports emanating from the interior of China, make mention that the disease known as Kinderpest in cattle is often found to precede an outbreak of plague.
Further, moist and rainy seasons are said to be productive of severe epidemics of the disease. Dr. ALEXANDER RENNIE in an interesting report on the occurrence of plague in Canton and the surrounding country, arrived at certain important conclusions as to the spread of the disease. In his opinion, rats contaminating food, overcrowding, filth, and bad drainage are responsible for the occurrence and persistence of plague in South China. He notes another important factor that thousands of natives disembark in Hongkong daily from the various river steamers, junks, etc., and that there is no medical supervision or inspection of such individuals. Modern scientific prophylaxis includes such a supervision and inspection among rudimentary principles.
The following avenues of infection are of importance in plague :-
1. The skin.
2. The respiratory tract.
3. The digestive tract.
1. The Skin. The unbroken skin offers the greatest resistance to the pass- age of all micro-organisms. Even a resistance to chemical reagents is most
pronounced,
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