SPORE-FORM A TION. 65 



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 condi- 

 tions favorable to germination, 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 be kept in a dry 

 state, and this has actually been done, for years without 

 losing the power of germination. The glistening, en- 

 veloping spore-membrane is not of uniform thickness 

 throughout, and in consequence when germination oc- 

 curs the growing bacillus, the so-called vegetative 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 in some way converted directly into a 

 vegetating cell. It evinces no motion other than the 

 mechanical tremor common to all insoluble microscopic 

 particles suspended in fluids, and it remains quiescent 

 until there appear conditions favorable to its subsequent 

 development. Occasionally the membrane of the vege- 

 tative cell in which the spore is formed does not disap- 

 pear from around it, and the spore may then be seen 

 lying in a very delicate tubular envelope. Now and 

 then, remnants of the envelope may be noticed ad- 



5 



