

beginning of the culture £^:~'o,\ ; is, they began from the 



moment of inoculation. An observation period, however, need 

 not begin with the beginning of the culture period and may 

 not be continued to the end of the culture period. Thus two 

 observation periods may be numerically alike, say 2 days, but 

 they may still have entirely different relations to the be- 

 ginning of the culture period, so as to constitute, in a 

 sense, distinct duration conditions. For example, all other 

 environmental conditions being supposed to be maintained, we 

 may determine the growth-rate for the 2-day period, beginning 

 with the second day after inoculation and also for the 2-day 

 period beginning with the fifth day after inoculation. The 

 mean daily rates derived from these two observation periods 

 are very apt to be markedly different. Cf course this state 

 of affairs is to be related to changes that go on wi thin the 

 organism, with the lapse of time, even though all physical 

 and chemical environmental conditions are assumed to be main- 

 tained without alteration. The organism is not exactly the 

 same at the moment of inoculation of a culture as it is a 

 day later, four days later, etc. Thi3 consideration intro- 

 duces one of the most perplexing features of the whole study 

 of maintained temperatures as related to vital processes, and 

 considerable attention will be devoted to it in the later 

 sections of this paper. 



From the points mentioned in the preceding paragraphs 

 it is, of course, clear that no very definite knowledge of the 

 various environmental influences, as they act to control the 



11 



