FORM AND CLASSIFICATION OF BACTERIA. 21 



glucose, or an acid, or alkaline reaction likewise may affect 

 the appearance of the cell. 



A comparison of the growths on solid and on liquid 

 media will show peculiarities and modifications in the form 

 and size of a given species. Thus, single cells' or at most 

 short threads may predominate on solid media, whereas in 

 liquid media very long threads or filamentous growths may 

 be found. 



The temperature exerts a profound effect upon the 

 form characteristics of bacteria. At low temperature the 

 growth is slower, and hence the individual cell may attain 

 an unusual size, whereas at a higher temperature multipli- 

 cation results so rapidly that the cells are considerably 

 smaller. 



Under unfavorable conditions of soil or temperature 

 certain bacteria will show remarkable variations from the 

 normal type. What is ordinarily a perfect rod becomes 

 distorted out of all semblance to the original form. Club- 

 shaped, spindle-shaped, dumb-bell-like forms are produced. 

 Sometimes they become twisted into irregular, spherical 

 bodies. These peculiar, deformed cells are considered as 

 degenerations. They are commonly designated as involu- 

 tion forms. The organism is struggling for existence under 

 adverse conditions which, if they persist, will eventually 

 cause its destruction. Transplantation to a favorable 

 medium will promptly restore the typical form. 



FIG. 3. Involution forms. 



The alterations mentioned above are the result of 

 environment. Whatever may be the variation, it is to be 

 considered always as temporary, inasmuch as the typical 



