78 MICROORGANISMS AND FERMENTATION. 



only filaments exceed this. The conditions of nutriment play 

 an important part in determining the shape of any one species. 



In all probability bacteria exist of such small dimensions 

 that they cannot be distinguished with existing microscopes. 

 Thus, Roux has shown that, in pleuro-pneumonia of cattle, 

 an organism occurs which develops colonies on the substratum, 

 while it is impossible, even with the strongest power, to see 

 the individual bacteria. 



A single species of bacteria may occur in various forms, 

 and this may happen either during the normal growth of 

 the vegetation,* or in growths on different media. Cases 

 also occur in which the same species may yield different 

 vegetative forms, which by prolonged cultivation under 

 different conditions give rise to so-called varieties. Isolated 

 cells occur in the growth of many bacteria which differ from 

 the rest in that they are irregularly swollen or branched ; 

 these have been named involution forms (Fig. 16). In some 

 species such cells represent a diseased growth possibly a 

 consequence of harmful ingredients in the culture medium 

 and they occur more particularly in old cultures ; in other 

 species, for instance the acetic acid bacteria, they appear, on 

 the contrary, to belong to a certain stage of the vegetative 

 growth. 



The bacterial cells contain protoplasm, a homogeneous, 

 feebly refractive substance, which may contain bright little 

 granules. Occasionally one or more clear spaces are found 

 within the cell, which by analogy with the higher plants are 

 regarded as sap-cavities or vacuoles. By staining. Rayman 

 and Kruis have rendered dark round bodies visible in the 

 centre of certain bacteria, which they named ceU nuclei. 

 The granules that occur in the plasma are, without doubt, 

 of very varied character, even in one and the same cell. In 

 many bacteria, fat globules have been distinguished with 



* As an excellent example of the regular occurrence of different forme, the 

 common hay bacillus will serve (B. subtilis). From the spore a motionless rod 

 develops which subdivides, the new individuals being transformed into swarming 

 cells. These then grow into very long, motionless threads which subdivide, and, 

 in each individual, one spore forms which is finally set free by the breaking down 

 of the surrounding cell walL 



