CHAPTER XXV. 



Study of bacterium anthracis, and of the effects produced by its inocu- 

 lation into animals Peculiarities of the organism under varying 

 conditions of surroundings Anthrax vaccines Anthrax immune 



THE discovery that the blood of animals suffering 

 from splenic fever, or anthrax, always contains minute 

 rod-shaped bodies (Pollender, 1855 ; Davaine, 1863), led 

 to a group of investigations that have not only fully famil- 

 iarized us with the nature of this malady in particular, 

 but have perhaps contributed more incidentally to our 

 knowledge of bacteriology in general than studies upon 

 any other single infective process or its causative agent. 



The direct outcome of these investigations is that a 

 rod-shaped micro-organism, now known as bacterium an- 

 thracis, is always present in the blood of animals suffer- 

 ing from this disease'; that this organism can be obtained 

 from the tissues of those animals in pure cultures ; and 

 that such artificial cultures of bacterium anthracis when 

 introduced into the bodies of susceptible animals can 

 again produce a condition identical with that found in 

 the animal from which they were obtained. The dis- 

 ease is a true septicaemia, and after death the capil- 

 laries throughout the body are always found to contain 

 the typical rod-shaped organism in larger or smaller 

 numbers. 



This organism, when isolated in pure culture, is a 

 bacterium which varies considerably in length, ranging 

 from short rods, 2 to 3 // in length, to longer threads, 

 20 to 25 fj. in length. In breadth it is from 1 to 



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