CHAPTER IV 



THE SIZE OF THE CELLS OF BACILLUS MEGATHERIUM 



While it has been well known for a long time that in old cul- 

 tures the form of the cells is different from that which they ex- 

 hibit in younger cultures, it has been only relatively recently de 

 monstrated that in very young cultures, that is during the active 

 growth period, there is also a difference in the cells from those in the 

 standard twenty-four-hour culture. This was demonstrated by Clark 

 and Ruehl, who have shown that during the early hours of growth 

 there occurs a marked increase in size of the cells with most species 

 of bacteria. They observed this in Bacillus typhosus, B. paratypho- 

 sus, B. colt, B. influenzcc, B. pyocyaneus, B. pertussis, B. anthracis 

 B. subtilis, B. vulgatus, B. avisepticus, and the cholera vibrio. The 

 same thing was observed with Streptococcus pyogenes, but not with 

 the glanders organism, the diphtheria bacillus, Hoffman's bacillus or 

 Bacillus xerosis, the last four showing a decrease rather than an in- 

 crease in the size of the cells. They note that the change in the 

 size of the cells is in some instances so great "as to render the organ- 

 ism unrecognizable when viewed by the ordinary standards of the 

 twenty-four-hour culture." They found that with a large number 

 of the cultures studied there was some increase in size apparent after 

 two hours incubation, the maximum size being reached on the aver- 

 age from four to six hours after inoculation. They state that "the 

 correlation in time of the occurrence of the long, coarse forms, with 

 the period when the maximum growth of the culture is taking place, 

 is obvious. That the cross section of the culture with its very short 

 average generation time should show a majority of forms dividing 

 and nearly ready for further^ division, is also obvious." This latter 

 statement, however, cannot be accepted. If the increase in size is 

 to be explained merely by the growth required for the cells to attain 

 a sufficient length for division to occur, that is twice their original 

 size according to our previous conceptions of the process, then the 

 maximum size attained should never be more than one and one-half 



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