16 BIOLOGY AND TECHNIQUE 



lack of nutrition, frequently seem to constitute the stimuli which lead 

 to sporulation. In the case of some species, notably the anthrax bacillus, 

 spores are formed only in the presence of free oxygen and are therefore 

 never formed within the tissues of infected animals. It is claimed that 

 some of the pathogenic anaerobes, like B. tetani and the bacillus of 

 malignant edema, may form spores anaerobically. Nevertheless it has 

 been observed that when an absolute exclusion of oxygen is practiced 

 in the cultivation of these bacteria, vegetative forms -only are seen in 

 the cultures. 1 



The process of sporulation is by no means to be regarded as 

 a method of multiplication, since it rarely occurs that a single bacil- 

 lus produces more than one spore. In some species of bacteria the 

 formation of several spores in one individual has occasionally been, 

 observed, but there can be no question about the fact that such a 

 condition is exceptional. 



Varieties of spores are often recognized, the so-called arthrospores 

 and the true spores or endospores. It is seriously in doubt whether the 

 structures once spoken of as arthrospores should be considered as in any 

 way comparable to true spores. They are represented by the granular 

 and globular appearances occasionally observed in old cultures of some 

 bacteria, notably streptococcus, cholera spirillum, diphtheria bacillus, 

 and others. It was believed that they were due to a transformation of 

 certain individuals of the cultures into more resistant forms. It is 

 probable, however, that such structures are merely to be regarded as 

 evidences of involution or degeneration, since it has never been demon- 

 strated that cultures containing them are more resistant either to dis- 

 infectants or to heat, than cultures showing no evidences of such forms. 

 The true spores or endospores are most common among bacilli, and 

 are rarely observed among the spherical bacteria. They arise within 

 the body of the individual bacterium as a small granule which probably 

 represents a concentration of the protoplasmic substance. Nakanishi 2 

 claims that there is a definite relation between these sporogenic globules 

 and the nuclear material of the bacterial cell. At the time at which 

 sporulation occurs there is usually a slight and gradual thickening of the 

 bacillary body. After the formation of this thickening, a spore mem- 

 brane appears about the same thickened area. The completed spore is 

 usually round or oval, has an extremely high refractive index, and a 



iZinsser, Jour. Exp. Med., viii, 1906, p. 542. 

 2 Nakanishi, Munch, med. Woch., 1900, p. 680. 



