PRINCIPLES OF VETERINARY SURGERY 103 



estimated, but the growth is usually arrested either by the 

 exhaustion of the nutrition or by the repressing effect of 

 metabolic products they elaborate in the environment. 



In addition to reproduction by fission some bacteria form 

 spores which ripen, split open and liberate the young organ- 

 isms. The spore develops within (endospore) the bacter- 

 ium, which degenerates as the spore enlarges toward 

 maturity. The process is called sporulation, and the micro- 

 organism reproducing itself by this process is referred to as 

 a sporogenic bacterium. Sporulation is one of the processes 

 by which bacteria preserve their existence when threatened 

 with destruction. It is not their usual mode of reproduction. 

 The newly-hatched bacterium liberated from the spore 

 develops into its characteristic form and then proceeds at 

 once to reproduce itself by fission. Sporulation is a mode of 

 self-preservation, while fission is the real mode of reproduc- 

 tion. 



Fig. 4. 

 Bacilli (1) and Cocci {2) Undergoing Binary Division. 



The formation of arthrospores, which consists of the 

 transformation of the entire bacterium into a spore, is a 

 mode of self-preservation that is known to exist in some few 

 species of cocci and small bacilli. It is a transformation 

 forced upon a bacterium through the influence of an en- 

 vironment unfavorable for its preservation. 



CULTIVATION OF BACTERIA.— In the study of 

 any given bacterium it is absolutely essential that it be sepa- 

 rated from its associates and a pure culture obtained ; other- 

 wise its special characteristics cannot be -accurately deter- 

 mined. One organism may destroy the products of another, 

 will change the reaction of the media, arid will in various 

 ways so inhibit the propagation of the microbe under surveil- 



