90 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



granules. In the first case, the ends of bacilli are stained more deeply 

 than the center so that the cells appear very much as diplococci.. This 

 bi-polar stain is characteristic of such organisms as the bacterium of 

 chicken cholera or the bacterium of bubonic plague. The polar 

 granules are frequently seen in the diphtheria bacterium and may 

 be located at the poles and also at the center. In this germ and in 

 some others it is possible, by special staining, to give the granules a dif- 

 ferent color from the rest of the organism. In this case these bodies are 

 spoken of as metachromatic granules which are considered later under 

 "Reserve Products." The presence of these granules might possibly 

 be explained upon the theory that the cells are plasmolyzed (Fig. 69). 

 As a result of plasmolysis the protoplasm of the cell is drawn away 

 from the cell wall and concentrated in areas which would very well 

 explain the appearances. And it seems likely also that the methods 

 employed in staining might lead to plasmolysis, but the metachromatic 

 granules can hardly be explained upon this supposition. 



The cytoplasm of the bacterial cell is slightly refractive. It is 

 colorless except in a few cases in which the green coloring matter, like 

 chlorophyl, is present, as, for instance, Bact. mride and Bad. chlorinum. 

 In the purple sulphur bacteria, the coloring matter bacteriopurpurin 

 is present. The bacterial cytoplasm contains vacuoles at times. 



MINUTE CONSIDERATIONS OF CYTOPLASM AND NUCLEUS.* The 

 question of the cytology of bacteria has long excited the curiosity 

 of biologists. It is indeed. of great importance from many points 

 of view. In the first place, we are interested to know whether 

 bacteria are ordinary cells having a nucleus; or whether, as some 

 maintain, they lack entirely a nuclear element and are an exception 

 to the rule elsewhere established. Moreover, the cytologic study 

 of bacteria may furnish useful knowledge concerning the phylogeny 

 and taxonomy of these organisms, a matter not yet solved. Finally, 

 we may hope that it will throw light upon some problems of a physio- 

 logical or pathological nature. 



Unfortunately this study is very delicate, because of the extreme 

 minuteness of the bacterial cells, so that in spite of the large number of 

 researches which it has incited in the last twenty-five years, it is to this 

 day a matter of controversy. 



At present three theories are held by authors relative to the inter- 

 pretation of the general structure of bacteria. We will examine these 



Prepared by A. Guilliermond. 



