(;i-:\ERAL CHARACTERISTICS OF BACTERIA 29 



The determination of morphological characters for the description 

 of bacteria should always be made from fully developed cultures; those 

 which are too young may present, as already noted, immature forms, 

 due to rapid multiplication, while in old cultures altered or degenerated 

 forms may be observed. 



A .Vlien growth is obtained upon different media, variations, especially 

 in size, may sometimes be observed. These differences should always 



FIG. 10 FIG. 11 



? /"'" 



- 



be described, together with a note of the media upon which they were 

 developed and a statement as to whether such variation is a marked 

 feature of the species under consideration. 



The conditions of temperature and of nutrition which favor growth 

 are very various for different species, so that no fixed temperature, 

 medium, or age of growth can be determined upon as applicafjle to all 



FIG. 12 FIG. 13 



-d 



{c 



Structure of bacterial cells. Plasmolysis : a, spirillum undula ; 6, bacillus solKusii ; c, vibrio 



(After BUtschli.) cholene. (After A. Fischer.) 



species. Morphological descriptions should always be accompanied 

 by a definite statement of the age of the growth, the medium from 

 which it was obtained, and the temperature at which it was developed. 

 Structure of Bacterial Cells. When examined in water under the 

 microscope bacteria appear merely as colorless refractile bodies w r ith 

 or without spores. It is only through using special stains that w r e are 

 able to see more of their structure (Fig. 12). They are thus found to 



