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(1.) Through the respiratory channels.-In cases of primary pneumonic plague, such a mode of elimination is of the highest importance. Hoards of plague bacilli are expired or expectorated by such patients, and the spread of in- fection may be occasioned either directly by so called drop infection, or indirectly through other channels. The question of communication of plague infection by this means has already been dealt with in another section of this research. cases of complicating consolidation of the lung in septicemic plague, the sputum is also found teeming with plague bacilli Whether the bacilli contained in such a sputum would effect an equally great chance of infection is a matter of doubt.
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Again in cases of ordinary septicemic plague apart from lung complications, there is reason to believe that occasionally plague bacilli may reach the outer world through such a channel as the sputum.
It would be advisable to regard all saliva and sputum of plague patients as sources of great danger.
In cases of plague, the disinfection of all matter discharged per os, ought to be a matter of ordinary routine.
(2.) Through the faces. In animals suffering from plague, the type of disease is septicemic, and the disorder is called forth with the greatest of certainty through the gastro-intestinal tract. The B. pestis in animals is more or less constantly found in the fœces. In the rat, this is especially the case.
In man, there is much evidence in favour of an alimentary incorporation of plague infection. The symptoms presented during life, coupled with the patholo- gical changes met with post-mortem and the bacteriological demonstration of the presence of plague bacilli in the foeces during life and the intestine after death, are much in favour of the gastro-intestinal tract being at least one of the principal foci of entrance of the B. pestis into the tissues of man The presence of diarrhoea, constituting the evacuation from the bowel of considerable quantities of fluid or semi-fluid material, is an element of great danger. The condition is analogous to that found during the first half of an attack of enteric fever.
Again the vomit must be treated with suspicion. Plague bacilli have been found in these discharges from the stomach. WILM and other writers make men- tion of the presence of the B. pestis in this fluid.
Like the sputum, therefore, all discharges from the gastro-intestinal tract, ought to be systematically disinfected, as these constitute elements favouring the spread of the disense.
(3.) Through the urine-This mode of elimination would perhaps come bet- ter under indirect methods of the discharge of the infection That plague bacilli are frequent contents of the urine has been firmly established. The condition is similar to that found in typhoid fever and other diseases. It is doubtful in such a thing as a typical plague bacteriuria is ever found. Probably an explanation similar to that which obtains for the occurrence of typhoid bacteriurin is applicable to plague, namely, the passage of stray plague bacilli through the tubules of the kidney and their appearance in the urine. It is known that the B. pestis resists the action of minute traces of acid for some considerable time. The urine of plague patients ought to be disinfected in all cases.
(4.) Through discharging buboes. It is generally believed that the younger the bubo, the purer the culture of the B. pestis found therein. Secondary infection of such bubonic swellings soon occurs. How soon, is difficult to say, and likewise, the true explanation of the effect of the micro-organismal association, namely, plague barilli plus pyogenic bacteria, is difficult to give. It is well known that the latter grow luxuriantly to the extermination of the former, and that in well marked suppurating plague buboes, plague bacilli are difficult to find.
It would be inter sting to determine, how far these secondary infecting or ganisms go in the production of the typical plague bubo with its spreading and far reaching hæmorrhagic extravasation.
In general terms, it may be stated, that secondary infection with pyogenic bacteria occurs during the earliest stages of bubonic formation.
The B. pestis is abundant during the first stages of the bubo. During the later stages, the B.