44 



MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



to bulge with the formation of a barrel-shaped organism, or a dostridmm. 

 If the spore is situated at the poles and is larger than the mother cell, a 

 capitate or drum-stick bacillus is produced. When the spore is smaller 

 than the mother cell and the cells form in chains, there is frequently a 

 tendency for the spore to be formed in opposite ends of contiguous cells 

 of the chain so that they appear in pairs. The reason for this is not 

 understood. 



The endospores possess remarkable powers of resistance due to the 

 concentrated character of the protoplasm, or to the character of the 

 spore wall. The resistance here may be due to the structure of the wall 

 itself or to the chemical substances which it contains. It is readily con- 



FIG. 23. The formation of 

 spores. (After Fischer from 

 Frost and McCampbell.) 



^3 



FIG. 24. Spores and their location in bacterial 

 cells. (After Frost and McCampbell.) 



ceivable that the presence of certain fatty acids, or higher alcohols, might 

 give the spore its remarkable resistance. These spores are very resistant 

 to desiccation; they have been preserved in a dried condition for many 

 years. They are also very resistant to the action of heat; some forms are 

 known to withstand a temperature of boiling water for as long a time even 

 as sixteen hours. They are resistant also to chemicals and the action of 

 sunlight. Although in some cases, as pointed out by Marshall Ward, 

 the very chemical substances which furnish them the powers of resistance 

 towards environmental factors may be broken up under the influence 

 of sunlight, forming poisons so that the spore is killed more readily 

 than the cell would be. 



When these spores are brought under favorable conditions of moisture, 

 temperature, and food supply, they germinate. There are several types of 

 germination (Fig. 25). In some cases the spore wall ruptures at the 



