THE STRUCTURE OF THE BACTERIAL CELL 3 



were formerly grouped together in one class as the Schizophyta qr 

 splitting plants. And of the two divisions forming these Schizophyta the 

 splitting algse were denominated the schizophycese, while the bacteria or 

 splitting fungi were called the schizomycetes. The bacteria were, there- 

 fore, often spoken of as the schizomycetes. This classification in its 

 reference to splitting fungi reflects the view, now practically abandoned, 

 that the bacteria represent the last stage of a progressive degeneration 

 which parasitism has entailed in the fungoid plants. 



General Morphology op the Bacteria. 



The Structure of the Bacterial Cell. — When examined under 

 the microscope, in their natural condition, e.g., in water, bacteria 

 appear merely as colourless refractile bodies of the different 

 shapes named. Spore formation and motility, when these exist, 

 can also be observed, but little else can be made out. For 

 their proper investigation advantage is always taken of their 

 affinities for various dyes, especially those which are usually 

 chosen as good stains for the nuclei of animal cells. Certain 

 points have thus been determined. The bacterial cell consists 

 of a sharply contoured mass of protoplasm which reacts to, 

 especially basic, aniline dyes like the nucleus of an animal cell. 

 A healthy bacterium when thus stained presents the appearance 

 of a finely granular or almost homogeneous structure. The 

 protoplasm is surrounded by an envelope which can in some 

 cases be demonstrated by overstaining a specimen with a strong 

 aniline dye, when it will appear as a halo round the bacterium. 

 This envelope may sometimes be seen to be of considerable 

 thickness. Its innermost layer is probably of a denser con- 

 sistence, and sharply contours the contained protoplasm, giving 

 the latter the appearance of being surrounded by a membrane. 

 It is only, however, in some of the higher forms that a definite 

 membrane occurs. Sometimes the outer margin of the envelope 

 is sharply denned, in which case the bacterium appears to have 

 a distinct capsule, and is known as a capsulated bacterium {vide 

 Fig. \, h; and Fig. 58). The cohesion of bacteria into masses 

 depends largely on the character of the envelope. If the latter 

 is glutinous, then a large mass of the same species may occur, 

 formed of individual bacteria embedded in what appears to be. a 

 mass of jelly. When this occurs, it is known as a zooglcea mass. 

 On the other hand, if the envelope has not this cohesive property 

 the separation of individuals may easily take place, especially 

 in a fluid medium in which they may float entirely free from 

 one another. Many of the higher bacteria possess a sheath 

 which has a much more definite structure than is found 



