18 BIOLOGY AND TECHNIQUE 



the spore body with a loss of its highly refractile character and resist- 

 ance to staining fluids. The developing vegetative cell may now 

 rupture and slip out of the spore membrane at one of its poles, leav- 

 ing the empty spore capsule still visible and attached to the bacillary 

 body. Again, a similar process may take place equatorially instead 

 of at the pole. In other species again, there may be no rupture of 

 the spore membrane at all, the vegetative form arising by gradual 

 elongation of the spore and an absorption or solution of the mem- 

 brane which is indicated by change in staining reaction. Division by 

 fission in the ordinary way then ensues. 



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,' 

 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 (sarcinse). 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 mutxially 

 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 fur- 

 nish a characteristic of great aid in differentiation. Similarly among 

 the bacilli there are forms which appear characteristically as single 

 individuals and others which form chains of varying length. 



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

 also with the favorable or unfavorable character of the environment. 

 A generation, that is, the time elapsing in the interval between one 



' Nakanishi, Cent. f. Bakt., I, xxx, 1901. 



