112 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 address before the International Medical Congress of Ber- 

 lin (1890) Koch says : 



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

 methods of staining and in spite of the use o 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 cell membrane in certain species appears to be very flexible, 

 as may be seen in those which have a sinuous motion. It is not 

 easily recognized under the microscope, but by the use of reagents 

 which cause the protoplasm to contract may be demonstrated e.g., 

 by iodine solution. Outside of the true cell membrane a gelatinous 

 envelope so-called capsule is sometimes seen. This may perhaps 

 be, as claimed by some authors, nothing more than a jelly-like thick- 

 ening of the outer layers of the cell wall. This jelly-like material 

 causes the cells to adhere to each other, forming zooglcea masses. 

 In some cases the growth upon the surface of a culture medium is 

 extremely viscid, and may be drawn out into long threads when 

 touched with a platinum needle, owing to the gelatinous intercellular 

 substance by which the cells are surrounded. 



There is but little more to be said of the structure of these minute 

 organisms, except to mention the fact that the motile species are 

 provided with slender, whip-like appendages called flagella. The 

 micrococci in general are not endowed with the power of executing 

 spontaneous movements, and they are not provided with flagella. 



