60 MORPHOLOGY 



the stain is distributed throughout the cell. There are also 

 portions of the cell which in some species do not stain (achro- 

 matic). Some writers hold the view that the chromatic 

 substance is nuclear material. The nuclear material has, 

 therefore, a general distribution throughout the cell. This is 

 undoubtedly true in the light of present research. Some bac- 

 teria, for example certain vibrios, consist almost entirely of 



chromatin. The amount of chromatic material varies a great 



. 



deal even in the same species under different conditions. It 

 has been suggested that the reason the nuclear material is not 

 aggregated in the regular form of the nucleus may be ascribed 

 to the fact that the bacteria are low in the stage of evolution, 

 and that they divide so rapidly that the nuclear material does 

 not have sufficient time to form itself into the resting stage which 

 the normal nucleus represents. Biitschli studied certain large 

 forms of bacteria which contain sulphur granules (Beg- 

 giatoaceae), and he concluded that the large part of the cell 

 was nucleus surrounded by a thin layer of protoplasm. Fischer 

 is inclined to believe that Biitschli's preparations were due to 

 plasmolysis. Nakanishi claims he has demonstrated a defi- 

 nite nucleus in the cells of some species of bacteria. This 

 observation has not been confirmed. 



Chemical Structure of the Bacterial Cell. Our knowledge 

 of the exact and complete chemical constitution of the bacterial 

 cell is at present quite as limited as our knowledge of the his- 

 tological structure. It may be said that bacteria are exceed- 

 ingly labile, and therefore the ordinary analytical methods 



