70 BACTERIOLOGY 



only of a cell-membrane and a transparent, clear space 

 which surrounds the spore. Eventually both the cell- 

 membrane and its fluid contents disappear, leaving the oval 

 spore free; it then gives the impression of being surrounded 

 by a dark, sharply defined border. When thus perfectly 

 developed, the spore may be regarded as analogous to the 

 seeds of higher plants. Like the seed, it evinces no evidence 

 of life until placed under conditions favorable to germina- 

 tion, when there develops from it a cell identical in all 

 respects with that from which it originated. Its tenacity 

 of life, as in the case of seeds, is almost unlimited. It may 



Fig. 6 



T(!' v^ >t -\r- 



,^ 



a b e d 



a. Bacillus subtilis with spores; 6, bacillus anthracis with spores; a, Clos- 

 tridium form with spores; d, bacillus of tetanus with end spores. 



be kept in a dry state, and this has actually been done, for 

 years without loss of viability. 



The glistening, enveloping spore-membrane is not of 

 uniform thickness throughout, and in consequence when 

 germination occurs the growing bacillus, the so-called vege- 

 tative form of the organism, protrudes through the thinnest 

 part of the spore-membrane — that is, through the point of 

 least resistance. This may be either the end or the side of 

 the spore, according to the species under observation. In 

 certain cases such a protrusion is not observed, but in its 

 place the spore in toto appears to be gradually absorbed or 



