12 



BIOLOGY AND TECHNIQUE 



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sent structures in any way comparable to spores, since cultures con- 

 taining individuals showing metachromatic granules are not more 

 resistant to deleterious influences than are others. Their abundant 

 presence in young vigorous cultures may indicate a relationship between 

 them and the growth energy of the microorganisms. There is no proof, 

 however, that these bodies affect the virulence of the bacteria. 



Cell Membrane and Capsule. — ^Actual proof of the existence of a cell 

 membrane has been brought in the cases of some of the larger forms 

 only,i but the presence of such envelopes may be inferred for most 



bacteria by their behavior during 

 plasmolysis, where definite retrac- 

 tion of the protoplasm from a 

 well-defined cell outline has been 

 repeatedly observed. The occur- 

 rence, furthermore, of so-called 

 "shadow forms" which appear as 

 empty capsules, and of, occasion- 

 ally, a well-outlined cell body, 

 after the vegetative form has en- 

 tirely degenerated in the course 

 of sporulation, make the assrnnp- 

 tion of the presence of a cell 

 membrane appear extremely well 

 founded. Differing from the cell 

 membranes of plant cells, cellulose 

 has not, except in isolated instances, been demonstrable for bacteria, 

 and the membrane is possibly to be regarded rather as a peripheral 

 protoplasmic zone, which remains unstained by the usual manipula- 

 tions. Zettnow,^ who has carefully studied the structure of some of 

 the larger forms, takes the latter view, and regards the "ectoplasmic" 

 zone as a part of the cell protoplasm devoid of nuclear material. Zett- 

 now's opinion is borne out by the greatly increased size of the bacterial 

 cells as seen by means of special stains. 



Many bacteria have been shown to possess a mucoid or gelatinous 

 envelope or capsule. According to Migula,' such an envelope is present 

 on all bacteria, though it is in only a few species that it is sufficiently 

 well developed and stable to be easily demonstrable and of differential 



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Fig. 2. — Bacterial Capsules. 



' Biitschli, loc. cit. " Zeltnow, loc. cit. 



' Migula, "Systeme d. Bakterien," 1, p. 56. 



