20 MICRO-ORGANISMS AS PARASITES. 



who have made the subject their special study : — " The tubercles 

 of leprosy, formed by a solid, dense, dermic tissue, are made of 

 large cells filled with bacteria. Tlic layers of the epidermis are free 

 from parasites, but are (from pressure) becoming constantly 

 thinned. So long as it is preserved, the layer of epidermis opposes 

 the diffusion of the parasite outwards, and constitutes a barrier 

 to its progress. It renders contagion very difficult." When, how- 

 ever, the thinned epidermis gives way, and an open ulcer is 

 formed, it is easy to see how readily fatal contagion might arise if 

 there were the slightest cut or other injury to the epidermis of a 

 person coming in contact with a leper. 



The bacillus of leprosy has not yet been cultivated outside the 

 human body, nor is it communicable to the lower animals. It 

 has taken possession of its human host so long, that it is 

 apparently not to be found in a wild state (if I may be allowed 

 the expression). Many of the larger parasites of man and the 

 lower animals pass their whole cycle of existence in or on their 

 host, so the lepra bacillus forms no exception in nature. 



In spite of all evidence existing to the contrary, many persons 

 will doubtless continue to refer leprosy to some unknown cause, 

 rather than believe it owes its origin to a bacillus universally 

 found in this disease and in no other, from Norway to China, and 

 from Honolulu to San Francisco, in cold climates and in hot, in 

 wet soils and in dry. I am tempted to say with rj)ante, " Non 

 ragionam di lor, ma guarda e passa." I am not aware that any 

 other strictly human parasite is invariably fatal to life ; glanders 

 is always, and anthrax usually, fatal to life, but the micro-organisms 

 of these diseases reside normally in animal hosts, and only by 

 accidental contagion prove fatal to man. 



I come now to a disease which, terrible as have been its ravages, 

 experience proves can be guarded against with extraordinary 

 success. I speak of Asiatic cholera. When it first came with giant 

 strides from the east, thousands upon thousands of human beings 

 were its helpless victims. The resources of medical skill seemed 

 exhausted ; the most apposite remedies were tried, and all failed 

 alike. Men knew not how to grapple with the terrible new foe. 

 Amongst the simple and superstitious peasants of Brittany, the 

 cholera was thought to be brought by demons, which the 



