50 BACTERIOLOGY. 



character of the fluid in which the bacteria are located ; in 

 fact, the deeply staining grannies, other than those of fat, 

 starch, and sulphur, that are often observed, are regarded 

 by some writers (especially A. Fischer) as but altered or 

 condensed protoplasm due to the same influences. 



In certain species the protoplasmic body is always 

 more dense at the poles of the cells than at the middle, 

 so that when stained the ends are much darker than the 

 intervening portion. Sometimes in other species the 

 reverse is the case. 



By some investigators the protoplasmic central mass 

 is regarded as a nucleus, and, functionally speaking, 

 possibly it is to all intents and purposes, but this cannot 

 be certainly decided. In the great majority of cases, 

 however, with the ordinary methods of examination, it 

 is not seen to possess any of the structural peculiarities 

 that we are accustomed to regard as the distinguishing 

 attributes of cell-nuclei. 



The enveloping hull or membrane is in some cases 

 apparently only a modification of the protoplasmic cen- 

 tral mass, at times being only a condensation of that 

 protoplasm ; again, it seems to be chemically different 

 from it. In a few instances it appears to be allied to 

 cellulose in its chemical composition. Sometimes it is 

 so thick as to be readily seen, while again it is discerni- 

 ble only by special methods of examination. In partic- 

 ular species it may, by appropriate methods, be seen as 

 a sharply defined capsule inclosing a clear zone in which 

 the deeply stained central mass lies. Occasionally the 

 central protoplasmic mass is surrounded by an ill- 

 defined slimy material that causes the individual cells 

 to adhere to one another in more or less compact masses 

 or pellicles (zoogloea, Fig. 1), 



