48 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



MINUTE STRUCTURE OF THE BACTERIAL CELL. 



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 structure in the cy- 

 toplasm, such as nucleolus, polar bodies, etc. In addition to these there 

 may be appendages, such as the cilia or flagella. In the case of the bac- 

 terial cell, we find most of these structures present, such as cell wall, 

 cytoplasm, and appendages, but the nucleus is either wanting or is so 

 modified in form as not to be recognized as an ordinary nucleus. 



BACTERIAL CELL WALL. Structure. All the bacteria have cell 

 walls and it is these that give rigidity to the cell. These walls are rigid 

 and elastic and are probably made up of two layers, the outer one is able 

 to deliquesce and form capsules, or perhaps zooglcea. The inner part re- 

 tains the elasticity and gives the form to the bacteria. These cell walls 

 are readily permeable to water and it is through them that all of the 

 nourishment of the cell is obtained; that is, there are no openings for 

 the entrance of food or the discharge of by-products, but the in- 

 take and output goes on through the cell wall which is entire. The 

 chemical nature of the cell wall is generally protein in nature and in this 

 respect perhaps resembles the animal cell wall more closely than it does 

 the plant cell wall, though many of the bacterial walls resemble those of 

 molds and some fungi. These cell walls take the ordinary stains with 

 difficulty, or not at all, and it is because they do not stain that they are 

 not seen. The ghost figures, frequently seen, are the walls of dead 

 mother cells from which spores have escaped. 



Capsules. A considerable number of the bacteria regularly, or under cer- 

 tain conditions, form what are known as capsules (Fig. 29). These are mu- 

 cilaginous envelopes which in width frequently exceed that of the organism 

 itself. In microscopical preparations of bacteria it is important to differ- 

 entiate these from artifacts, since by ordinary staining methods the capsules 

 are not colored but appear as colorless areas surrounding the bacteria. 

 If, due to shrinkage of the bacteria, or other material on the preparation, 

 clear spaces are formed, it is readily seen that these might be confused with 

 the real capsule. It is possible to stain the capsules by special methods; 

 these must be used in order to determine positively the existence of the 

 capsules. The material of which the capsules are composed is derived 

 from the cell itself, probably the result of the deliquescence of the outer 



