120 MORPHOLOGIC VARIATION 



of cells characteristic of the growth phase, the resting phase, and 

 the death phase, respectively; the first being large, relatively plump, 

 and straight, the second being more slender and markedly curved, 

 the third being characterized by asymmetry of the cells. 



The variations in size of the cells were relatively slight as com- 

 pared with the variations noted previously in Bacillus megatherium 

 and the colon bacillus. The mean length of the cells is given in 

 Table XXV. There was a slight increase beginning at six hours, 

 that is at the end of the lag period, which persisted to practically 

 the end of the resting period (forty-eight hours), after which the 

 cells showed a considerable decrease in length. Clark and Ruehl, 

 however, found that the cholera vibrio showed an increase in length 

 of cells of practically the same degree as that noted with the other 

 organisms that they studied, and it is quite possible that in my 

 observations the change in the size of cells is not as great as is 

 usually the case. No studies of frequency distribution of the cells 

 with regard to their size have been made with this organism. 



More significant results were obtained from the study of the 

 variations in form by means of the area-length index. These are 

 given in Table XXIV. No pronounced variation occurred until 

 after nine hours, corresponding approximately with the point of in- 

 flection between positive and negative acceleration in growth rate. 

 After this period the area-length index decreased considerably, reach- 

 ing its minimum at eighteen hours, which corresponds with the point 

 of inflection between the growth phase and the resting phase, after 

 which it again increased, remaining fairly constant at a high level 

 during the death phase. Slendemess of the cells is, then, a charac- 

 teristic of the resting phase, and plumpness a characteristic of the 

 death phase. When plump cells are used for seeding, the latter 

 half of the growth phase is occupied by a progressive increase in 

 their slenderness. 



While the area-length index serves to measure the cells with re- 

 gard to their relative slenderness or plumpness, it does not take 

 care of another variation in form characteristic of the cholera vibrio, 

 namely the degree of curvature of the cells. This, however, can 

 be simply determined by measuring the length of the cells (by 

 means of dividers) along their major axis (L^) and the shortest 



