28 THE MORPHOLOGY OF BACTERIA 
plasm usually stains readily with basic anilin dyes. A few bacteria, 
notably B. viride and B. chlorinum, contain a yellowish pigment in 
the cytoplasm suggesting chlorophyll, anfl 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 
cannot be separated chromoscopically into a nucleus and cytoplasm. 
Those who have thoroughly studied the question by staining methods, 
notably Nakanishi,^ 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 nuclear substance is distributed 
throughout the cell in very finely divided granules. Zettnow- 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 
morphological nucleus demonstrable by ordinary staining methods 
nuclear material is present in abundance in the organism. Putter^ 
has shown, also, that the electrophoretic behavior of bacteria corre- 
sponds quite closely to that of nuclei of animal cells. 
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. Schumacher^ 
claims that these granules are composed largely of free nucleic acid. 
In the hemorrhagic septicemia group these granules are arranged 
S3'mmetrically, 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 composition. Some bacteria contain granules which are 
colored brown with iodine, suggesting that they may be related to 
1 Centralbl. f. BakterioL, 1901, 30, 97, 145, 193, 225. 
2 Ztschr. f. Hyg., 1899, 30, 1; Festschr. z. 60 Geburtstage von R. Koch, 1903, p. 383. 
3 Zeitschr. f. Immunitat, 1921, 32, 538. 
" Centralbl. f. BakterioL, I Abt. Orig., 1922, 88, 362. 
s Ztschr. f. Hyg., 1889, 5, 428. 
6 Ibid., 1S89, 5. 173; 1895, 20, 412. 
