36 VETERINARY BACTERIOLOGY 



size until it occupies a portion only of the space within the cell 

 wall, and has then surrounded itself with a heavy wall, probably 

 chitinous in nature. In practically all cases there is but one 

 spore in a cell. The spore may be equatorial or polar in position, 

 and of less or greater diameter than the cell which produces it. 

 The term dostridium is sometimes used to indicate a spore-bearing 



Fig. 14. Development of endospores in a bacillus. (After Fischer.) 



rod in which the spore is equatorial and of greater diameter than 

 that of the cell, resulting in a spindle. Endospores contain only 

 about 20 per cent, of water as compared with 80 to 90 per cent, 

 in the cells which produced them. An organism without a spore 

 is usually differentiated by the term vegetative rod or vegetative 

 cell. Spores are much more resistant to desiccation, heat, light, 

 and chemicals than the vegetative cells. They are of use in 



Fig. 15. Bacterial spore types: A, Equatorial spores of a diameter less 

 than the cell; B, polar spores of a diameter less than the cell; C, equatorial 

 spores of a diameter greater than the cell (clostridium type) ; D, drumstick or 

 polar spores of a diameter greater than the cell. 



tiding the organism over unfavorable conditions. Spore-bear- 

 ing bacteria are abundant in the soil, where they often are exposed 

 to great ranges of moisture, temperature, and light. When a 

 spore again comes under favorable conditions for growth, it 

 germinates and produces a cell typical of its species. Germina- 

 tion is accomplished either by stretching or bursting the spore 

 wall. 



