SPORES AND SPORULATION .23 



cell-chain, but they possess none of the essential properties of a spore. They 

 are simply detached vegetative cells without special powers of resistance 

 and destitute of any lasting germinative faculty. Another kind of arthro- 

 spore is said to occur in the case of Leuconostoc, where certain cells generally 

 larger than their neighbours surround themselves with a very thick mem- 

 brane, and without further preparation enter the ' resting stage.' Similar 

 cases occur among the blue-green algae, but are quite unknown among 

 ordinary bacteria. What have been described as arthrospores in bacteria (in 

 cholera cultures, for instance) are in all probability nothing but deeply- 

 staining granules from the detritus of old cultures. They have never been 

 seen to germinate. Bacterial arthrospores, if the term were justified, would 

 be of the same shape as the vegetative cells of the species to which they 

 belonged ; the cholera arthrospore appearing as a curved refringent rod, 

 that of B. violaceus as a straight cylinder, &c. 



Of the causes which bring about sporulation very little can be said. 

 As with other organisms, it seems to be induced by an unfavourable environ- 

 ment, arrest of food supply, or the accumulation of the excretory products 

 of the bacteria themselves. In pathogenic forms, at least in those cases 

 that have been carefully studied, spores are not produced so long as the 

 bacteria are enclosed within the diseased tissues. The anthrax bacillus 

 forms them only in places where there is free access of air — in the excre- 

 tions of diseased cattle, for instance, or on the surface of the carcase ; never 

 inside it, either before or after death (see also Chap. XVI). 



