THE REPRODUCTION OF BACTERIA. 33 



stances to be mentioned later, what are known as spores are 

 formed by a number of bacilli and spirilla. These spores, 

 which are perhaps the equivalents of seeds for the higher 

 plants, are formed in this way : in the body of the bacillus, 

 generally at its centre, occasionally at one of its poles, a 

 number of dark highly refractile granules accumulate, and 

 are soon changed into an oval, glistening, highly refractile 

 body which is surrounded by a membrane of the same com- 

 position as that of the cell itself, but thicker and more 

 resistant. One spore only is formed in each cell. Some- 

 times the spore-formation causes no change in the shape of 

 the rod. At other times there is a bulging of the centre of 

 the body of the bacillus, where the spore is located, with a 

 general tapering to the two ends, giving to the bacillus the 

 shape of a spindle. This is called a clostridium. Again, 

 when the spore is formed at one of the poles, there is some- 

 times a bulging of that part, giving to the bacillus the 

 appearance of a nail or drum-stick, whence the name of drum- 

 mer-bacillus for the cell. Fig. 7 shows these forms well. 



FIG. 7. 



Q 



a. Bacillus siibtilis with spores, b. Bacillus anthracis with spores, c. Clostridiumform 

 with spores, rf. Bacillus of tetanus with endospores. (Abbott.) 



Soon after the formation of the spore the rest of the body 

 of the cell disintegrates and breaks down, and the oval spore 

 is liberated. 



The spores are characterized, on account of their thick 

 membrane, by resistance to external influences which would 

 be fatal to the bacilli themselves, such, for instance, as 

 extremes, of heat or cold, desiccation, and the action of chemi- 

 cals ; also, to a great extent, staining by the penetration into 



3 M. B. 



