INFECTIOUS DISEASES AND MICROBES, ETC. 181 



when this attenuated virus is introduced into the 

 body by inoculation, it produces a mild type of 

 yellow fever,-and confers immunity against the fatal 

 type of the disease. From 1883 to 1890 Freire l has 

 inoculated 10,881 persons in Brazil with cultures of 

 M. amaril. The mortality of those so vaccinated 

 was 0'4 per cent., although the patients lived in 

 districts infected with yellow fever, whilst the 

 death-rate of the uninoculated during the same 

 period was from 30 to 40 per cent. 



Yellow fever is distributed (within certain areas) 

 by moist winds and human intercourse. "Water and 

 the soil have nothing to do with the spread of the 

 disease, although it is a disease which clings to the 

 ground, hence one of the reasons of its endemic 

 nature. It is always prevalent in the plains near 

 the sea-coast, and along the courses of the great 

 rivers. Heat (21 C.) and a certain saturation of 

 the atmosphere are essential conditions for an 

 epidemic of yellow fever. Frost puts an end to an 

 epidemic at once, and storms, heavy rains, or cold 

 weather check its progress. 



HYDROPHOBIA. 



Hydrophobia or rabies is a canine disease, which 

 is communicated by a bite, and the inoculation of 

 man and other animals by the saliva. The exact 

 nature of the microbe of this disease is not yet 

 known. According to Pasteur, 2 Fol, 3 Babes, 4 and 



1 Comptes Rendus, 1889 and 1891, 2 Comptes Rendus, 1884. 



3 Ibid., 1885, p. 1276 ; Le* Microbes, 1885, p. 41. 



4 Les Bacteries, 1890, p. 550. 



