BACTERIA 



of the spore in the cell varies (Fig. 64). In some species it is equatorial, 

 in others it is polar, and in still others it has an intermediate position 

 between equatorial and polar. When the spore is larger than the 

 mother cell and is situated equatorially it causes the cell to bulge with 

 the formation of a barrel-shaped organism, a clostridium. 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 spores 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. When the spore has reached maturity, the mother cell 

 disintegrates and finally disappears, leaving the endospore free. 



The endospores possess remarkable powers of resistance due to the 

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



j 



FIG. 63. 



FIG. 64. 



FIG. 63. The formation of spores. (After Fischer from Frost and McCampbell.) 

 FIG. 64. Spores and their location in bacterial cells. (After Frost and McCampbell.} 



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- 

 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 chem- 

 icals 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 toward environmental factors may be 

 broken up under the influence of sunlight, forming poisons so that the 

 spore is killed more readily than the vegetative cell would be. 



