20 MORPHOLOGY 



Ruzicka (1898, 1903, 1908, 1909) regarded the whole bacterial cell as homologous 

 with the cell-nucleus of more highly developed organisms. There is no substantial evidence, 

 apart from a similarity of staining reactions, for identifying the bacterial cell as nucleus, 

 and, even if there were so, the term nucleus would be a misnomer, for, as DobeU points 

 out, a nucleus must by definition be dififerentiable from the cytoplasm of the ceU. 



Meyer (1897, 1899, 1908) has been a prominent exponent of the view that bacteria 

 contain weU-defined nuclei and has brought together the available evidence in his book 

 on the bacterial cell (1912). Many other observers have shared this view (Feinberg 

 1900, Nakanishi 1901, Ellis 1902-03, 1922, Grimme 1902, Swellengrebel 1906, Amato 

 1909, Vay 1909, 1910), but it is reasonably certain that the structures observed differed 

 in their nature, so that the observations do not confirm one another. The observations 

 of Mencl (1904, 1905, 1909, 1910) and of Rayman and Kruis (1904) strongly suggested 

 the presence of a differentiated nucleus in the bacteria they studied. Their earlier observa- 

 tions have not been confirmed ; according to GuiUiermond (1907) the structures they 

 describe as nuclei were stages in the formation of transverse septa. Stoughton (1929, 

 1932) found in a plant pathogen, Bad. malvacearum, a central nucleus-like body differ- 

 entiable from the cytoplasm by intravitam staining. The constancy of its occurrence, 

 position, and division during cell division suggested a true nucleus. Guilhermond (1933) 

 identified the body as a volutin granule (see below). In one case, the observation by 

 Vejdovsky (1900, 1904) of a nucleus in an organism he named B. gammari, there is a 

 consensus of opinion that a true nucleus has be«n demonstrated, but there is good reason 

 to believe that the organism itself is a fungus, not a bacterium. 



There remain several possibilities, of which we may mention three : that the nuclear 

 material is diffusely and uniformly scattered through the cytoplasm, that it is disposed 

 in certain chromatin masses in the cytoplasm, and that there is in the cell a separate nuclear 

 apparatus, perhaps consisting of one or more chromosomes, not usually revealed by 

 ordinary staining methods. 



The notion of the diffuse nucleus has arisen partly to explain the absence of a demon- 

 strable discrete nuclear body (Zettnow 1918), and partly to account for the occurrence 

 of a uniform coloration of some bacteria when treated by Feulgen's reagent. Feulgen's 

 reagent is used as a test for thymonucleic acid. A diffuse Feulgen reaction of' bacteria 

 lias been noted by a number of observers (see, for example, Pietschmann and Rippel 

 1932, Imsenecki 1936). Knaysi (1938) doubts the specificity of the reaction, and points 

 out that if nucleic acid is demonstrated in this way, it may be merely reserve material in 

 the cell, having no necessary connection with a nuclear apparatus (see also Schaede 

 1939, Musky 1943, Stedman and Stedman 1943). As we have seen, Lindegren (1935) 

 objects to the conception of a diffuse nucleus on genetical grounds ; it is necessary to 

 assume the existence of some form of discrete nuclear body, which, by dividing into 

 identical halves, can ensure the genetical constancy of the daughter ceUs. The view 

 that nuclear material is segmented in certain chromatin masses in the ceU has been developed 

 by Schaudinn (1902) in the case oi B. biitschlii, by GuiUiermond (1907) in the case of several 

 cultivable spore-bearing bacilli, and by DobeU (1911) in the case of bacilli parasitic in 

 reptiles and fishes. 



Schaudinn described numerous small chromatin-like granules, which were scattered 

 through the cytoplasm of B. biitschlii, a large spore-bearing bacillus. At the start 

 of sporulation, the granules gather into an axiaUy situated spiral. The ends of the 

 spiral increase in size at the expense of the chromatin granules, and develop into homo- 

 geneous masses that stain deeply with nuclear stains. These masses, as they develop 

 into spores, cease to take up the stain, and generally appear as highly refractile unstained 

 bodies. GuiUiermond (1907) foundasimUar picture in the spore-bearing baciUus studied 

 by him. Cells eight hours old were finely vacuolated, and contained numerous granules 

 of chromatin. At sporulation, however, no axial filament was formed, and a single deeply 

 staining mass appeared at one pole of the cell, gradually increasing in size. DobeU (1911) 

 observed scattered chromatin that was gathered into an axial filament before sporulation 



