Microbial Structures and Staining Reactions 97 



2. The entire cell is composed of cytoplasm with no nucleus. 



3. There is a definite nucleus in bacterial cells but the usual stain- 

 ing technics do not reveal a nucleus except when the cells are 

 grown under specific conditions, and stains are made at a precise 

 stage in their growth. 



4. Chromatin granules are spread out in the cytoplasm and are 

 abundant enough to give the impression that the entire cell is 

 composed of chromatin material. 



This latter theory of a diffuse nucleus has considerable support 

 in the bacteriology profession. Blue-green algae have such a 

 nuclear structure, but because these bodies are larger than in 

 bacteria, they are more readily observed under the microscope. 

 Electron microscope studies have revealed distinct nuclear-like 

 material in some bacterial species and undifferentiated nuclear 

 matter in still other cells. By adhering to the structure definition 

 of a nucleus, it must be admitted that bacteria probably have no 

 nucleus. But if function is considered, all cells must have a 

 regulatory body, and bacteria are probably no exception. From 

 the functional point of view, the structure of the nucleus is of 

 relatively little importance. 



CAPSULES AND SHEATHS 

 Although it is not possible to demonstrate capsules on all 

 bacteria, it may be a safe assumption that all bacteria possess a 

 slime layer, sometimes of a thickness not detectable by the usual 

 technics employed for their demonstration. There is evidence that 

 capsules serve as a protective material for some organisms, by 

 slowing down or preventing penetration of chemicals and body 

 juices. Most capsular material is carbohydrate or carbohydrate- 

 like in nature, but lipoid material predominates in a few selected 

 species. The capsule may be a mere thickening of the outer 

 membrane or more probably a secretion or excretion which deposits 

 itself around the cell. Capsule formation can be enhanced by 

 animal passage of certain organisms or by growing them in high 

 carbohydrate media. 



