SPORING BACILLI 305 



occurs late in the disease ; in animals, on the contrary, the 

 blood-invasion is early. 



The Algerian sheep and the white -rat have a high degree 

 of immunity. Pollender first described the anthrax 

 bacillus as occurring in the blood of animals succumbing 

 to splenic fever. Rayer and Davaine repeated the 

 observation in 1850 (a year later) ; Brauell, in 1857, found 

 the bacilli in the blood of a man affected with anthrax, 

 and Davaine gave everything but absolute proof that they 

 were the exciting cause of anthrax. Koch, by succeeding 

 in getting a pure culture on the aqueous humour of an ox's 

 eye, was able to prove its specificity. He also added 

 largely to the knowledge of its life-history, and particularly 

 to the mode of formation of spores. 



Description. B. anthracis is a straight rod, non-motile, 

 with square or concave ends, 4-5 to 10 micra long by i to 

 1-5 micron thick ; forming chains in cultures, and sporing 

 by oval spores one to each rod ; placed about the centre of 

 the bacillus, and of about the same diameter, and highly 

 refractile. Gram-positive ; gelatin-liquefying, and said at 

 times to possess a capsule when recovered from tissues or 

 blood, or grown on latter. 



Cultures. Grows well on all media, best at 37-5 C., 

 but also from 12 to 45 C. 



In broth : a heavy flocculent sediment, slight pellicle, 

 remainder clear. 



In gelatin stab : an invreted fir-tree growth, with gradual 

 fluidification. 



In gelatin plate : colonies develop within 24 to 48 hours 

 as opaque white pin-head discs, later becoming larger and 

 less regular, and under the microscope showing a hair-like 

 tangle of threads the so-called Medusa head. 



In agar plate : the colonies magnified thirty times show 

 wavy wreaths like locks of hair, the whole colony being 

 probably one long thread. Such colonies are very suit- 

 able for making impression preparations, and in such the 

 wreaths are seen to be made up of bundles of long filaments 

 lying parallel with one another, each filament consisting of 

 a chain of bacilli. 



On potato : a thick white felted mass, useful for studying 

 porulation. 



2O 



