THE NUCLEUS 67 



1903), who looked upon the observed granules as reserve materials 

 rather than nuclear substance. Migula (1894, 1897, 1904) regarded the 

 existence of nuclei in bacteria as very doubtful. The majority of workers, 

 on the contrary, have held that a nucleus or at least nuclear material is 

 present in some form. The most striking view is that which regards the 

 whole cell in some cases as a naked nucleus (Hiippe 1886; Zettnow 1891, 

 1897, 1899; Ruzicka 1908, 1909; and, in the case of small bacteria, 

 Biitschli.1890, 1892, 1896, 1902). The evidence advanced in support of 

 this hypothesis, however, is of very doubtful value. 



In many bacteria, particularly the larger forms, there is present a 

 granular substance which has certain characteristics of chromatin, and 

 which in some species exists as a single well defined mass. The "central 

 body" of the sulphur bacterium Biitschli regarded as the homologue of a 

 nucleus, the peripheral portion of the cell being cytoplasm. In a careful 

 study of the entire life cycle of Bacillus Butschlii Schaudin (1902) found 

 that the chromatic material present during most of the cycle as chromidia 

 unites at certain stages to form peculiar spiral figures; in the spores it 

 takes the form of dense masses. Such scattered chromidia and "spiral 

 filament nuclei" were also observed by Guilliermond (1908, 1909), who 

 has given a review of the subject (1907). Nakanishi (1901), who employed 

 both intra-vitam methods and fixed material, reported the presence of 

 nuclei in the vegetative cells and spores of a number of species. 



The nucleus of the large Bacterium gammari was studied by Vejdow- 

 sky (1900), who in 1904 described its division by mitosis. Mencl (1904, 

 1905, 1907, 1909) demonstrated by careful methods the nuclei in many 

 species and also reported mitotic division in Bacterium gammari. Doubt 

 concerning the systematic position of this form, however, has been raised 

 by some investigators, who think it not improbable that it is a yeast- 

 like fungus rather than a bacterium. 



Dobell (1908, 1909, 1911), whose review of the subject has been of 

 service in the preparation of this summary, has studied with much care 

 many species of bacteria in their natural culture media. His conclusions 

 are summarized in the following quotation (1911): 



"All bacteria which have been adequately investigated are like all 

 other Protista nucleate cells. 



"The form of the nucleus is variable, not only in different bacteria, 

 but also at different periods' in the life cycle of the same species. 



"The nucleus may be in the form of a discrete system of granules 

 (chromidia); in the form of a filament of various configuration; in the 

 form of one or more relatively large aggregated masses of nuclear sub- 

 stance; in the form of a system of irregularly branched or bent short 

 strands, rods, or networks; and probably also in the vesicular form char- 

 acteristic of the nuclei of many animals, plants, and protists. 



"There is no evidence that enucleate bacteria exist." 



