MORPHOLOGY, REPRODUCTION, ETC. 19 



cleavage and the next, has been estimated by A. Fischer 1 as being 

 about twenty minutes for the cholera spirillum and 16-20 minutes for 

 bacillus coli communis, under the most favorable conditions. The same 

 author has calculated that under these ^ conditions a single cholera 

 spirillum would yield 1600 trillions in a single day. Such a multiplica- 

 tion rate, however, is probably not usual under natural or even artificial 

 conditions, both on account of lack of nutritive material and because of 

 inhibition of the growth of the bacteria by their own products. 



VARIATIONS OF BACTERIAL FORMS 



Variations from the basic forms considered in the preceding sec- 

 tion may occur, but are not common among bacteria under normal 

 conditions. Thus the formation of club shapes by a thickening of the 



FIG. 6. DEGENERATION FORMS OF BACILLUS DIPHTHERIA. (After Zettnow.) 



bacillary body at one or both ends has been frequently observed among 

 bacteria of the diphtheria group, and in the glanders bacillus, and an 

 irregular beading is not infrequently observed in tubercle bacilli under 

 normal conditions. Such pictures can not, in these cases, be regarded 

 as degeneration or involution forms, since they are visible in young, 

 actively growing cultures under ordinary conditions. It is a well-known 



1 A. Fischer, " Vorlesungen iiber Bakt.," Jena, 1903. 



