BACTERIOLOGICAL TECHNIQUE. 229 



influenza bacilli, reach the maximum development of 

 their colonies in from ten to sixteen hours, while others 

 continue to spread for several days. If we wait too long 

 where numerous varieties of bacteria are growing the 

 colonies of heavier growth may cover up the finer and 

 more delicate ones. As a rule, the younger colonies 

 are more characteristic, except where the development 

 of pigment is sought. 



FIG. 30. 



Two surface colonies of diphtheria bacilli upon agar. X 500 diameters. 



The colonies are first examined with the eye (Fig. 28), 

 then with a low magnification, and then again at from 

 400 to 500 diameters (Fig. 30). We note everything 

 we can about them, such as their size, border, density, 

 color, and granular appearance. At the higher mag- 

 nification we begin to detect the individual bacteria. 

 After studying the colonies we remove a few of the bac- 

 teria from one or more of them by touching them with 



