MORPHOLOGY OF BACTERIA 61 



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 

 proteolytic 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. 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 ap- 

 parently only a modification of the protoplasmic central 

 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 discernible only by special methods of 

 examination. In particular species it may, by appropriate 

 methods, be seen as a sharply defined capsule inclosing a 



