50 BACTERIOLOGY. 



ticular species and under various conditions of growth 

 the central mass in stained specimens is commonly 

 marked by the presence of very dark granules, the 

 so-called metachromatic granulations. Again, in other 

 species paraplastic granules giving the microchemical 

 reactions of fat, starch, sulphur, etc., are to be seen. 

 Under certain physical conditions the protoplasmic body 

 presents irregular rents or retractions, the result of pro- 

 teolytic or of osmotic disturbances dependent upon the 

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

 fact, the deeply staining granules, 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 



