BACTERIA 



103 



by-products, but the intake and output goes on through the cell wall 

 which is entire. 



Minute Structure of Cell Wall.* In some species of large size, 

 the membrane can be distinguished when strongly magnified, and 

 appears with a double contour. Usually it is scarcely visible, and can 

 be observed only when the contents of the cell has been contracted by 

 plasmolysis or by a suitable reagent. It is sometimes thin, some- 

 times more or less thick. In the latter case, it is often possible to 

 recognize two layers, an inner or cuticular layer, very thin and trans- 

 parent; and the other external, not so well defined and thicker, jelly- 

 like in appearance. This latter or gelatinous layer seems to result 

 from a special differentiation of the peripheral zones of the inner layer. 

 The outer layer ordinarily resists staining reagents and appears as a 

 kind of transparent zone about the colored elements. It can acquire 

 a relatively great thickness, and the formations described as capsules 

 are only an exaggeration of this gelatinous layer. 



Schaudinn has been able to observe quite care- 

 fully the construction of the cuticular layer in 

 B. butschlii. According to him, the membrane 

 seen in profile would appear to consist of a 

 series of disks alternately clear and cloudy (Fig. 

 80, A and B). Seen from the front, it would 

 give the impression of a network whose meshes 

 are more refringent and stain more highly (C). 

 It is laid on a. peripheral zone of cytoplasm, a 

 kind of ectoplasm with closer network, and is 

 clearly differentiated from the rest of the cyto- 

 plasm. The spore is provided with a double 

 membrane and has at one of its poles a sort of 

 micropyle through which germination is effected 

 (Fig. 73, 15 and 16). 



The chemical composition of the membrane 



is little known. According to some authors, this membrane consists 

 of cellulose; according to others, it contains a lipoid substance; 

 finally, by many authors it is supposed to be composed principally 

 of nitrogenous compounds. Let us remark further that chitin has 

 supposedly been detected therein. 



* Prepared by A. Guilliermond. 



FIG. 80. A and B, 

 Structure of the mem- 

 brane and of the ecto- 

 derm in Bacillus 

 butschlii. C, Membrane 

 of the same bacillus, 

 front view. (After 

 Schaudinn.} 



