OBSERVATIONS OF DIPHTHEROID BACILLUS 107 



food material is based upon this observation. Albert states that in 

 the case of the diphtheria bacillus: 



Granules appear in cultures four to eight hours old. These are at first of 

 small size. Granules attain their largest average size in cultures twelve to 

 fifteen hours old. After this period the granules diminish in size and disappear. 

 The percentage of bacteria which contain granules increases rapidly from the 

 four-hour period when there are but a few granules to the twelve-hour 

 period when 91 per cent contain granules. At the end of two days most of 

 the bacilli have lost their granules. 



The curve for the mean number of granules per cell in Figure 28 

 shows that the granules rapidly disappeared with active growth, 

 the minimum number being found at nine hours (when there was 

 only one granule to every ten cells) , which corresponds approximately 

 with the point of maximum growth. But the granules came back 

 very slowly, not nearly so rapidly as was noted by Albert with the 

 diphtheria bacillus. This is probably due to a difference in the 

 nature of the organisms, though perhaps in part to the fact that 

 he was using a much more favorable medium and probably much 

 more heavily seeded than my cultures. 



The mere number of granules is not a very good measure of 

 the amount of volutin in the cells, since the granules also vary 

 greatly in size, in general being smallest when they are fewest, and 

 gradually increasing with age of the culture until they nearly, com- 

 pletely fill the cell. I have not noted their disappearance during 

 the late stages of growth as has been described by Albert; on the 

 contrary, they become more and more prominent, and very irregular 

 in form in the large filamentous and irregular cells found in old 

 cultures. 



It will be noted in Figure 28 that the curves for cell length 

 and for number of granules per cell follow the same general course, 

 the approximation being greater during the later stages of growth 

 than at the beginning, since the granules decreased at once, whereas 

 the cells did not begin to shorten until after some hours. There 

 is apparent then a degree of correlation between the size of the 

 cells and the number of granules which they contain. I have cal- 

 culated the coefficients of this correlation for the various samples 

 in which the granules were counted (100 cells were counted and 



