MORPHOLOGY, REPRODUCTION, ETC. 19 



REPRODUCTION OF BACTERIA 



Bacteria multiply by cell division or fission. A young individual 

 increases in size up to the limits* of the adult form, when, by simple 

 cleavage, at right angles to the long axis, without any discoverable 

 process of mitosis or nuclear changes, it divides into two individuals. 

 In spite of the claims of various bacteriologists, notably Nakanishi, 20 

 traceable analogy to the karyokinesis of other cells has not been 

 definitely established. In the case of the spherical bacteria a slight 

 change to the elliptical form takes place just before cleavage and 

 this cleavage may occur in one plane only, in two planes, or in three 

 planes. According to the limitations of cleavage direction, the cocci 

 assume a chained appearance (streptococci), a grape-like appearance 

 (staphylococci), or an arrangement in packets or cubes having three 

 dimensions (sarcinae). In the cases of bacilli and spirilla, cleavage 

 takes place in the direction of the short axis. The individuals, after 

 cleavage, may separate from each other, or may remain mutually 

 coherent. The cohesion after cleavage is pronounced in some species 

 of bacteria and slight in others, and, together with the plane of 

 cleavage, determines the morphology of the cell-groups. Thus among 

 the cocci diplo- or double forms, long chains and short chains may 

 arise and furnish a characteristic of great aid in differentiation. 

 Similarly among the bacilli there are forms which appear character- 

 istically as single individuals and others which form chains of vary- 

 ing length. 



The rate of growth varies to a certain extent with the species, 

 and also with the favorable or unfavorable character of the environ- 

 ment. A generation, that is, the time elapsing in the interval between 

 one cleavage and the next, has been estimated by A. Fischer 21 as 

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

 utes 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 

 multiplication rate, however, is probably not usual under natural or 

 even artificial conditions, both on account of lack of nutritive mate- 

 rial and because of inhibition of the growth of the bacteria by their 

 own products. 



20 Ndkanishi, Cent. f. Bakt., I, xxx, 1901. 



21 A. Fischer, ' ' Vorlesungen iiber Bakt.," Jena, 1903. 



