24 



MORPHOLOGY 



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to be numerous and of large size ; in others, they are scanty or absent. Some 

 species which seldom contain volutin granules frequently contain fat globules. 

 In others the presence of glycogen or starch is a characteristic feature. The data 



available do not warrant us in saying that any one 

 of these forms of granular material is the peculiar 

 property of certain species or is uniformly absent 

 from others, but their relative abundance or scar- 

 city may be a striking characteristic of a particular 

 bacterial species. 



For a good and concise account of these in- 

 tracellular granules see Zettnow (1918). 



Endospores. — The formation of intracellular 

 spores by bacteria was first observed by Cohn 

 (1875), and first studied in detail by Koch (1876) 

 in the case of B. anthracis. The fact that the 

 existence of an endospore, and its significance in 

 reproduction, had been clearly demonstrated in the 

 case of one of the first bacteria to be identified 

 as the cause of an important infective disease, led 

 many observers to approach the study of new 

 bacterial species with a bias towards identifying 

 any morphologically differentiated element within 

 the bacterial cell as a spore, or its equivalent. 

 Much of the earlier literature is, for this reason, 

 full of mistaken allusions to spores or sporogenous 

 granules in various bacteria. We now know that 

 the formation of endospores is an important dis- 

 tinguishing characteristic of certain bacterial groups. 

 The great majority of sporing bacteria which 

 have been adequately studied are monosporous, 

 that is only one spore occurs in any one cell. A 

 few large forms which have been observed by 

 cytologists are di-sporous. 



The mode of formation of the spore has been 

 briefly referred to in discussing the nuclear appar- 

 atus of the cell. There is general agreement that it 

 is formed by a localized accumulation of chromatin, 

 or of a chromatin-like substance, which at first 

 stains deeply with nuclear stains, but which later 

 becomes surrounded by a spore-wall or membrane, 

 which is impervious to stains in the absence of 

 special prehminary treatment ; so that the ripe 

 spore appears as an unstained, highly refractile 

 body, spheroidal or ovoid in shape. As regards the 

 finer details of spore-formation there is less agree- 

 ment, and it would seem possible that the process dii?ers to some extent in 

 dift'erent bacterial species. Many observers have described the appearance, at 

 the commencement of sporulation, of a clear vacuolar area, corresponding in 

 size and shape to the space occupied by the ripe spore, and the subsequent 



A 



Fig. 6. 



a-c. Without distortion of bac- 

 terial cell. 



a. Spherical equatorial. 



b. Oval equatorial. 



c. Oval subterminal. 



d-g. With distortion of bacterial 

 cell. 



d. Spherical terminal. 



e. Oval terminal. 

 /. Oval equatorial. 

 g. Oval equatorial. 



h and i. Germination of spores. 



h. Polar germination. 



t. Equatorial germination. 



