140 MORPHOLOGIC VARIATION 



vibrio as described in Chapter VIII there was at the beginning a 

 slight decrease in size and increase in area-length index. While these 

 were not in all cases associated with dormancy of the cells as regards 

 division rate, it seems to me that we are dealing with the same sort 

 of phenomenon; the cells do not immediately recover from the aging 

 influence which was present in the old culture. 



It would seem from my data that the division of the growth 

 curve into a lag phase (of accelerating growth), a logarithmic growth 

 phase, and a resting phase, is not so significant as a division into 

 a phase of accelerating growth and a phase of negative acceleration 

 in growth; the so-called logarithmic growth phase when present is 

 but a long drawn out point of inflection. For the morphologic 

 variations which occur during the early stages of growth progress 

 definitely to this "mid-point" (as Pearl designates it) of the growth 

 cycle, then turn sharply in the opposite direction. The embryonic 

 forms reach their maximum development just at the beginning of 

 negative acceleration in growth rate, the mature forms at the end 

 of growth. The transformation of aged cells to embryonic forms 

 precedes cell division; the initial period of dormancy then is occu- 

 pied in part (but only in part) by this transformation. The gradual 

 acceleration in growth rate is probably best explained by the nature 

 of the frequency distribution of the inoculated cells with regard to 

 their capacity for growth, as reflected in their frequency distribu- 

 tions with regard to those morphologic characters which distinguish 

 the embryonic forms. 



These embryonic forms will vary in their characters with dif- 

 ferent species of bacteria, but it is apparent from what has been 

 presented here, as well as from the observations of Clark and Ruehl, 

 that with most forms, especially the rods, they differ from the 

 mature forms particularly in increased length and slenderness. The 

 diphtheroid group are apparently an exception, the embryonic forms 

 being shorter and more nearly approaching the spherical form. In 

 all cases these embryonic forms seem to possess a higher affinity 

 for the basic aniline dyes. In those cases where the young cells 

 show an increased size there is also apparent an increased varia- 

 bility in size. In those forms which develop intracellular granules 

 or other structures these are lacking in the embryonic cells. In 



