74 3Ianual of Veterinary Microbiology. 



II. Reaction of the organism against microbes. 



"We will consider, successively, under this head : 

 phagocytosis, the bactericidal property, the isolation 

 and elimination of pathogenic microbes, and varia- 

 tions of virulence produced by the organism. 



When non-pathogenic germs, or germs in which 

 the virulence is extinguished, are introduced into the 

 tissues of an animal, these germs are more or less 

 quickly destroyed. The same thing occurs when 

 pathogenic germs in full virulence are introduced 

 into the system of an individual destitute of recep- 

 tivity for the germs. On the other hand, if the viru- 

 lent germs are brought into contact with an organism 

 endowed with receptivity they will multiply and be- 

 come the starting point of morbid troubles. 



There are, therefore, in the organism of certain ani- 

 mals, conditions capable of bringing about the de- 

 struction of microbes. These conditions are multiple 

 and their nature is as yet incompletely elucidated. 

 "We know, however, that the organism defends itself 

 against invasion through the intermediation of its 

 figured elements and of its fluid parts. 



1. Phagocytosis. — The name 'phagocytosis is given to 

 the destructive action of certain cells toward mi- 

 crobes, these cells being known as phagocytes. The 

 white corpuscles, in this regard, take first place in 

 whatever part of the body we find them : blood, con- 

 nective tissue, lymphoid organs (spleen, lymph glands, 

 marrow of bones, etc.) ; then come the fixed cells of 

 the connective tissue, the endothelial cells of the 

 capillary vessels, the cells of soft epithelia, muscular 

 fibers, etc. 



