12 BIOLOGY AND TECHNIQUE 



forms. As a matter of fact, the true nature of these bodies is by no 

 means certain. They are present most regularly in microorganisms 

 taken from young and vigorous cultures or in those taken directly 

 from the lesions of disease. It is unlikely that they represent struc- 

 tures in any way comparable to spores, since cultures containing 

 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 



y^_. ., ; <fc M 



FIG. 2. BACTERIAL CAPSULES. 



forms only, 11 but the presence of such envelopes may be inferred for 

 most bacteria by their behavior during plasmolysis, where definite 

 retraction of the protoplasm from a well-defined cell outline has been 

 repeatedly observed. The occurrence, 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 entirely 

 degenerated in the course of sporulation, make the assumption 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 pro- 

 toplasmic zone, which remains unstained by the usual manipulations. 



ll Butschli, loc. cit. 



