12 BACTERIOLOGY FOR NURSES 



temperature above the limit at which it grows best not only ceases 

 to form spores but it loses its power of sporulation. 



The second view is that a bacterium only forms spores when 

 conditions are unfavorable to its life and growth ; that it is essen- 

 tially a process whereby a species may be preserved in a hostile 

 environment until its surroundings again become favorable. The 

 lack of food, the presence of substances excreted by the bacteria 

 themselves, and the products formed by the disintegration of the 

 food material in which they are growing play an important part 

 in making unsuitable surroundings. Species which form spores 

 under these conditions will always change into vegetative forms 

 when placed in a fresh food supply. 



The tests usually made to determine whether or not spore 

 formation has taken place are : (1) Subjection of the culture to a 

 temperature high enough to kill vegetative forms without injuring 

 spores, (2) Microscopic examination for the presence of a refractile 

 body within the bacterium, which cannot be stained by ordinary 

 dyes but which can be colored by the special methods devised for 

 the staining of spores (page 30). 



Chemical Composition. The chemical composition of bacteria 

 varies somewhat according to the nature of the species and the 

 material upon which they are growing. Ordinarily the bodies 

 of bacteria contain from 80 to 88 per cent of water. Substances 

 of a protein nature similar to the albumins and globulins found in 

 animal and plant tissues are present which probably represent 

 the vitality of the cell. The presence of fat has been demonstrated ; 

 also starch-like granules staining blue with iodine have been 

 observed. Sulphur, iron, calcium, potassium, chlorin, magnesium, 

 etc., may also, in small quantities, form part of the bacterial 

 protoplasm. 



