BACTERIA 



lOI 



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

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

 recogmze two layers, an inner or cuHcular layer, very thin and trans- 

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

 Uke 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 reagpnts and appears as a 

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

 a relatively great tHckness, and the formations described as capsules 

 are only an exaggeration of this gelatinous layer. 



Sciiaudinn has been able to observe quite carefully the construction 

 of the cuticular layer in B. butscklii. According to him, tlie membrane 

 seen in profile would appear to consist of a 

 series of disks alternately clear and cloudy (Fig. 

 77, 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. 71, IS 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. 



Capsules * — A considerable number of the bacteria regularly, or 

 under certain conditions, form what are known as capsules (Fig. 78). 

 These are mucilaginous envelopes which in width frequently exceed 

 that of the organism itself. In microscopical preparations of bacteria 

 it is important to differentiate these from artifacts, since by ordinary 

 Staining methods the capsules are not colored but appear as colorless 



♦prepared by W. D. Frost, 



Fig. 77. — A and B, 

 Structure of the mem- 

 brane and of the ecto- 

 derm in Bacillus 

 hiitschlii. C, Membrane 

 of the same bacillus, 

 front view. {After 

 Schaudinn-) 



