118 STRUCTURE, MOTIONS, REPRODUCTION. 



vious drying ; the preparations were then stained with carbol-meth- 

 ylene-blue or carbol-fuchsin solution ; they were decolorized with 

 nitric acid and examined in glycerin or in water. By this procedure 

 the author named was able to demonstrate two kinds of corpuscles. 

 One of these may be seen just inside the cell wall ; it stains deeply 

 with the carbol-fuchsin solution. The other lies in a position analo- 

 gous to that occupied by the nucleus of vegetable cells higher in the 

 scale, and resembles this both in its resting condition and in the 

 process of indirect division. 



In his addross bofore the International Medical Congress of Ber- 

 lin (1800) Koch says : 



' We had not succeeded, in spite of the constantly improving 

 methods of staining and in spite of the use of objectives with con- 

 stantly increasing angles of aperture, in learning more with reference 

 to the interior structure of the bacteria than was shown by the origi- 

 nal methods of staining. Only very recently new methods of stain- 

 ing appear to give us further information upon the structure of the 

 bacteria, inasmuch as they serve to differentiate an interior portion 

 of the protoplasm, which should probably be regarded as a nucleus, 

 from an exterior protoplasmic envelope from which is given off the 

 organ of locomotion, the flagellum." 



Although usually transparent, the protoplasm sometimes presents 

 a granular appearance. The botanist Van Tieghem claims to have 

 found chlorophyll grains in some water bacteria studied by him, and 

 in the genus Beggiatoa grains of sulphur are found embedded in the 

 protoplasm of certain species. 



The granules in bacterial cells which may be demonstrated by 

 special methods of staining are of two kinds : metachromatic gran- 

 ules and polar granules. The former lie in the protoplasm, and 

 when properly stained may present the appearance of a short chain 

 of cocci lying in the bacterial cell. To demonstrate their presence 

 Ernst recommends the use of Loffler's solution of methylene blue. 

 This is placed upon a cover-glass preparation and heated over a 

 flame until steam begins to rise. After washing in water the cover 

 glass is placed for a minute or two in a watery solution of Bismarck 

 brown. This shows the granules stained blue and the surrounding 

 protoplasm brown. The polar granules are often seen in prepara- 

 tions stained in the usual way with an aniline staining solution. 

 Some observers have regarded these stained granules as spores, but 

 this has not been demonstrated, and cultures containing them show 

 no greater resistance to heat or to chemical agents than that estab- 

 lished for the vegetative cells of the particular species in which they 

 are found. It seems probable that the matachromatic granules re- 

 sult from degenerative changes rather than that they are reproduc- 

 tive bodies. 



