50 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



the microscope, in either an unstained or stained condition, it appears as 

 a homogeneous mass filling the entire cell and rarely showing any evidence 

 of structure. Ordinary stains, such as are used in animal and plant histol- 

 ogy, fail to reveal the presence of the ordinary nucleus, the whole cell being 

 usually uniformly stained with those stains ordinarily characterized as 

 nuclear stains. When these stains are applied to some bacteria, particu- 

 larly at certain stages of their growth, certain parts stain more readily than 

 others, and we get either what is known as a bi-polar stain or polar gran- 

 ules. 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 



I 



FIG. 30. Plasmolytic changes. (After A. Fischer.} a, cholera vibrio; b, typhoid 

 bacillus', c, Spirillum undula. (From Novy.) 



at the center. In this germ and in some others it is possible, by special 

 staining, to give the granules a different color from the rest of the organism. 

 In this case these bodies are spoken of as metachromatic granules. Whether 

 or not the bi-polar stains or the polar granules are evidences of structure 

 or not is an open question, since the results obtained might be explained 

 upon the theory that the cells are plasmolyzed (Fig. 30). 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 ex- 

 plained upon this supposition. They must be either special protoplasmic 

 structures or reserve food material, and for each of these theories there 

 are able supporters. 



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

 less except in a few cases in which the green coloring matter, like chloro- 

 phyl, is present, as, for instance, Bact. viride and Bad. chlorinum. In the 

 purple sulphur bacteria, the coloring matter bacteriopurpurin is present. 

 The bacterial cytoplasm contains vacuoles at times. 



