148 MORPHOLOGIC VARIATION 



different phases of growth. The diphtheriod organism which I have 

 studied, for instance, looks almost like a streptococcus in the period 

 of active growth, while it is a long, granular rod in the resting phase. 

 Now if this organism had been inoculated into different media, in 

 one of which it grew slowly and the other rapidly, and these were 

 compared, it would seem to the observer that the organism had 

 undergone a pronounced variation, and this would be apparent every 

 time the organism was subcultured on to these two media, other 

 conditions being the same. It is, therefore, necessary to determine 

 the phase of growth in every case where cultures are compared 

 with the view to establishing mutation. 



It should also be pointed out here that those who may attempt 

 to repeat my experiments must inoculate their cultures Hghtly, if 

 they will see the degree of morphologic variation in the early stages 

 of growth which I have described. By the ordinary procedure of 

 transferring from one agar slant to another, generally a loopful of 

 the organism is carried over. A culture so inoculated will have an 

 extremely short period of accelerating growth, during which only 

 slight change in cell size will be observed. The difference between 

 the embryonic forms and mature forms is quantitative, and this 

 difference becomes greater the higher is the actual rate of growth 

 attained. 



This chapter should not be closed without a word or two regard- 

 ing the relationship of these findings to problems of general bacteri- 

 ology. The morphologic variations described are but outward mani- 

 festations of equally profound variations in the physiology of the 

 organisms, concerning which we are practically in the dark. There 

 are scattered references in the literature to differences in degree of 

 virulence, of antigenic value, of susceptibility to antibody action, 

 or differences in fermentative power, between young and old cul- 

 tures; but in practically no cases have these variations in physiologic 

 properties been definitely correlated with phases of growth. It 

 would seem that this would offer an extremely attractive field for 

 investigation, especially from the standpoint of infection and im- 

 munity. Such investigations, however, are difficult to carry out, 

 because when the cells of bacteria are physiologically young, they 

 must necessarily be few in number in proportion to the volume of 



