BACTERIA 89 



CELL AGGREGATES AMONG THE SPIRILLA. The same kind of 

 arrangement is maintained among the spirilla. 



ZOOGLCEA. Some of the bacteria secrete a mucilaginous substance 

 which causes the cohesion of the cells frequently in considerable number. 

 This aggregate of cells may assume some characteristic appearance and 

 a great many attempts have been made by systematists to make use 

 of this in differentiating species. These zoogloeic masses usually 

 assume the forms of pellicles, but their value as diagnostic features is not 

 great. The formation of zooglcea is very frequently only a stage in 

 the life history of an organism. 



THE CYTOLOGY OF BACTERIA 



* The typical cell, such as that of a higher plant or animal, is made 

 up of cytoplasm surrounded by a cell wall. The cytoplasm contains a 

 nucleus. There are also frequently present other evidences of struc- 

 ture in the cytoplasm, such as nucleolus, polar bodies, etc. In addition 

 to these there may be appendages, such as the cilia or flagella. In 

 the case of bacterial cells, we find most of these structures present, 

 such as cell wall, cytoplasm, and appendages. 



GENERAL CONSIDERATION OF CYTOPLASM AND NUCLEUS.* The 

 cytoplasm of the bacterial cell is similar to the cytoplasm of other cells 

 except that chemical analyses seem to show that it contains a higher 



FIG. 69. Plasmolytic changes. (After A. Fischer.} a, Cholera vibrio; b, typhoid 

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



percentage of nitrogen. As viewed under 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 histology, fail 

 to reveal the presence of a nucleus, the whole cell being usually uni- 

 formly stained with those stains generally characterized as nuclear 

 stains. When these stains are applied to some bacteria, particularly 

 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 



Prepared by W. D. Frost. 



