OBSERVATIONS OF DIPHTHEROID BACILLUS 103 



of the same kind. The resting cells are large, with a faintly stained 

 protoplasm and deeply stained granules. When growth commences 

 they become much shorter, almost spherical in form, arranged in 

 chains; the granules disappear, and the entire protoplasm becomes 

 deeply stained. 



The results of the various measurements are presented graphically 

 in Figure 28, and in tabular form in Tables XIX, XX, and XXL 

 In Figure 28 the logarithms of the numbers of cells are plotted as 

 a solid line, the average length of the cells as a dotted line, and 

 the average number of granules per cell as a dot-and-dash line. 

 The measurements of cell length show very pronounced minor fluc- 

 tuations which must be due to experimental error, but the major 

 tendency is clear. During the period of accelerating growth rate 

 the size shows very little change; if anything, the cells increase 

 somewhat. But as soon as the growth rate begins to slow up there 

 occurs a very pronounced decrease in the size of the cells, which 

 reach their minimum size at about the point of inflection between 

 the growth phase and the resting phase. The return to the original 

 size proceeds very slowly; the original size is attained only after 

 the culture had been in the resting phase for some twenty-four 

 hours. Since the growth curve was determined by cell counts rather 

 than by plate counts, it is quite possible that the culture had entered 

 the death phase before the original size was reached. While measure- 

 ments were not continued longer than forty-eight hours, simple in- 

 spection of the slides shows that they continue to elongate, becoming 

 long filaments after some days. 



It will be seen at once that the variations in cell size with this 

 organism are of quite different nature from those found with B. 

 megatherium and the colon bacillus. It might be argued that the 

 slight initial increase in size apparent during the period of accelera- 

 ting growth is the same sort of a phenomenon as the pronounced in- 

 crease noted with the other two organisms, and that the pronounced 

 decrease during the period of negative acceleration is a peculiarity 

 of the diphtheroid group. In favor of this hypothesis is the fact that 

 the granules disappear and the protoplasm becomes rather deeply 

 stained before there occurs any decrease in the size of the cells. 

 But Clark and Ruehl failed to observe any initial increase in the size 



