BACTERIA AND DISEASE 301 



about four days show adult growth. The margin is un- 

 even, and the centre more opaque than the rest of the 

 colony. This diplococcus is readily killed, and sub-cultures 

 must be frequently made to retain vitality and virulence. 

 Light, desiccation, and a temperature of 55 C. all act germ- 

 icidally. The organism stains readily in Loffler's blue, but 

 is decolourised by Gram's method. It is more or less 

 strictly parasitic to man. Its shape, size, character of 

 growth, and staining properties assist in differentiating it 

 from various similar diplococci. 1 



Anthrax. This disease was one of the first in which the 

 causal agency of bacteria was proved. In 1849 Pollender 

 found an innumerable number of small rods in the blood of 

 animals suffering from anthrax. In 1863 Davaine described 

 these, and attributed the disease to them. But it was not 

 till 1876 that Koch finally settled the matter by isolating the 

 bacilli in pure culture and describing their biological char- 

 acters. 



It is owing in part to its interesting bacterial history, 

 which opened up so much new ground in this comparatively 

 new science, that anthrax has assumed such an important 

 place in pathology. But for other reasons, too, it claims 

 attention. It appears to have been known in the time of 

 Moses, and was perhaps the disease described by Homer in 

 the First Book of the Iliad. Rome was visited by it in 

 740 B.C. 



Anthrax is an acute disease, affecting sheep, cattle, 

 horses, goats, deer, and man. Cats, white rats, and Alger- 

 ian sheep are immune. Swine become infected by feeding 

 on the offal of diseased cattle (Crookshank). 



The post-mortem signs are mainly three: The spleen is 

 greatly enlarged and congested, is friable to the touch, and 

 contains enormous numbers of bacilli ; the skin may show 

 exudations forming dark gelatinous tumours ; and the blood 



1 See Trans. Jenner Institute (First Series), A. G. R. Foulerton, pp. 40-81. 



