442 G. S. WILSON 



logarithmic phase has been devised. So far, however, as the 

 latter part of the phase is considered, it is seen that the total 

 and viable curves do actually run very nearly parallel to one 

 another. Whether or no this hypothesis be correct it does at 

 least seem to explain how a dissociation of the total and viable 

 counts may occur, and how the logarithmic curve for the viable 

 count can yet ascend by means of a straight line — a fact which 

 has been substantiated by several workers independently. Of 

 course the actual percentage of the viable to the total is not con- 

 stant, the figures in the 16 experiments undertaken varjing from 

 57.86 to 122.8 per cent. Taking the arithmetic mean of the 

 percentage relations between the two counts at the end of the 

 logarithmic phase, the proportion in the 16 experiments came to 

 81.42 per cent. It seems justifiable to conclude therefore that 

 under the ordinary conditions of in vitro cultures of Bad. sui- 

 pestifer there is a normal death rate of approximately 20 per cent 

 per generation, with variations extending between 43 per cent 

 on the one hand to nil on the other. If this is actually so, it is 

 a very surprising fact — totally in disaccord with all previous 

 work on the subject. Translated into actual figures it means 

 that no fewer than 200 organisms in every 1000 produced are 

 dying in each generation. The old teaching has been accepted 

 for so long — namely, that during the logarithmic phase all the 

 bacilli are viable that one naturally feels diffident in contradic- 

 ting it; yet the figures quoted seem to admit of no other course. 

 Moreover, viewed from a general biological standpoint, it would 

 be surprising if all the progeny in a given species continued to 

 live and reproduce, however favorable the environment and how- 

 ever abundant the food supply. It seems to be very much more 

 in accordance with the principles of this science that a certain 

 proportion of each generation should fail to attain maturity and to 

 propagate their kind; what the actual cause of this may be is 

 difficult to ascertain, but the fact remains that in practically 

 every species studied there is a variation in the progeny leading 

 to the survival of some and the death of the others. 



