Page:Transactions of the Royal Society of Tropical Medicine and Hygiene, volume 2 (3).djvu/26

130 DISCUSSION How could they explain the local limitation of cutaneous inoculations in diseases such as variola, anthrax, tuber- culosis and kala-azar ? It had been suggested that the absence of tendency to generalization might be due to the special structure of the skin or to its lower temperature, and experiments had proved that adipose tissue and dense connective tissue were unfavourable to the propagation of pathogenic organisms. To these reasons others might be added. Thus it was quite likely that, in the case of pathogenic agents which had a wide zoological distribu- tion, a different zoological source might account for dif- ferences in virulence and location. That belief wa's founded not only on the observation of natural facts, but also on the result of experimental investigation. Bacte- riologists were constantly either exalting or attenuating the virulence of disease-producing microbes by successive passages through the organisms of different animals, and they had noticed again and again that microbes obtained from a diseased organ, when introduced into other animals, usually localized themselves in that part which had been attacked in the first subject.

In the case of Leishmaniasis, they knew that the infec- tion had been noticed in horses and dogs. In the dog, the cutaneous form had been early recognized in India, Persia, and Syria ; it presented itself almost invariably on the bare tip of the nose. The general infection had been demonstrated only quite recently by Nicolle in Tunisian dogs. Nicolle had not only found the " Leishraan- Donovan bodies " in the spleen and bone-marrow of stray local dogs, but had succeeded in reproducing the infection in other dogs by means of the inoculation of infected splenic blood into the liver and peritoneal cavity of normal puppies. Nicolle's experiments presented the objection of being carried out in a place in which dogs