STRUCTURE AND CONSTITUENTS OF BACTERIAL CELL 27 



B. chlorinum, contain a yellowish pigment in the cytoplasm suggesting 

 chlorophyll, and the so-called purple bacteria similarly possess a 

 purple colored pigment, bacteriopurpurin. 



Nucleus. The occurrence of a demonstrable morphological nucleus 

 in bacteria is by no means definitely settled: the typical bacterial 

 cell can not be separated chromoscopically into a nucleus and cyto- 

 plasm. Those who have thoroughly studied the question by staining 

 methods, notably Nakanishi, 1 believe that the whole bacterial cell, 

 as it is ordinarily seen, is potentially a nucleus surrounded by a very 

 thin film of cytoplasm. Others believe the nucleus substance is dis- 

 tributed throughout the cell in very finely divided granules : Zettnow 2 

 is the champion of the latter theory. He believes that the bacterial 

 cell, as it is viewed following the usual staining processes, is endoplasm 

 in which the nuclear substance is finely divided and uniformly dis- 

 tributed. Some observers deny that a nucleus exists at all. Chemical 

 analyses show beyond doubt that bacteria contain a relatively high 

 percentage of substances usually regarded as essentially of nuclear 

 origin. It is quite certain, therefore, that, although there may be no 

 morphologic nucleus demonstrable by ordinary staining methods, 

 nuclear material is present in abundance in the organism. 



Metachromatic Granules. Certain types of bacteria, notably mem- 

 bers of the diphtheria and hemorrhagic septicemia groups, exhibit 

 one or more highly refractile granules in an otherwise homogeneous 

 endoplasm when they are examined unstained with the higher powers 

 of the microscope. These granules are few in number in the diphtheria 

 bacillus group and are distributed somewhat irregularly throughout 

 the cell, one or more granules usually being greater in diameter than the 

 cell itself, thus giving the rod a swollen appearance. In the hemor- 

 rhagic septicemia group these granules are arranged symmetrically, 

 one at each end of the organism, polar granules. Such granules are 

 called Ernst-Babes or metachromatic granules. They color differently 

 from the rest of the cell when they are stained with methylene blue, 

 appearing as mahogany-red spots in the deep blue endoplasm. They 

 retain the stain rather tenaciously. Many theories have been advanced 

 to explain their significance, but nothing definite is known about them, 

 except that these granules appear to differ widely in chemical composi- 

 tion. Some are colored brown with iodine, suggesting that they may 

 be related to glycogen. 3 Some stain black with osmic acid, suggesting 



1 Centralbl. f. Bakteriol., 1901, xxx, 97, 145, 193, 225. 



2 Ztschr. f. Hyg., 1899, xxx, 1; Festschr. z. 60 Geburtstage von R. Koch, 1903, p. 383. 



3 A. Meyer, Flora, 1899, Ixxxvi, 428. 



