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- structure of the mem- 

 plasm. The spore is provided with a double brane and of the ecto- 

 , j i p ., i r derm in Bacillus 



membrane and has at one of its poles a sort of bMsc hUL C, Membrane 



micropyle through which germination is effected of the same bacillus, 

 /-r,. j ^\ front view. (After 



(Fig. 73, 15 and 1 6). Schaudinn.) 



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. 



