SECT. 2] AND WEIGHT 525 



after that a sustained high series until 25,000 is reached, followed by 

 a spurt at 27,000. In a word, the peaks of growth as a whole and 

 embryonic growth are very much alike, namely at 10,000, 20,000 and 

 27,000, but the middle one of these is specially associated with the 

 development of the embryo. Now there can be no doubt but that the 

 velocity of growth (reciprocal of the time required to attain a given 

 size or stage of development) can be expressed well in its relation 

 to temperature by the Arrhenius equation. Unfortunately, there is 

 difficulty in deciding what is the exact meaning of the frequency 

 with which the value of 20,000 occurs. There seems to be no reason 

 why this should be so usual a feature of the time/temperature 

 relation in embryos, and the modes at 10,000 and 27,000 are equally 

 mysterious. No doubt it may be expected that further work, both 

 in the direction of precision of data and in the direction of explana- 

 tion of the significance of these values, will clear the matter up. The 

 identification of the reactions responsible would certainly be a 

 desirable thing. At present there is only one suggestion as to the 

 meaning of a /i of 20,000, namely, its association by Glaser with 

 "mobilisation hydrolysis", i.e. the production of oxidisable sub- 

 stances by hydrolytic action such as the formation of glucose from 

 glycogen. The mode at 10,000 might be ascribed to synthetic processes, 

 but this would apply better to the growth-values of 7000 or thereabouts. 

 "I am quite unable to attach possible specific significance to tem- 

 perature characteristics 8000 and 27,000", says Crozier in a private 

 communication. "It will be realised that in the case of the earlier 

 statements one is dealing with somewhat uncertain suggestions of 

 which the chief value may be that they serve to suggest specific 

 experiments. I should personally tend to deplore theories of the 

 physico-chemical control of diflferentiation and development which 

 might very easily be erected on the basis of such speculation." In 

 these circumstances all that can be done is to note the values of fi 

 which have been so far obtained for embryonic growth without 

 attempting to give them any meaning. 



Perhaps the most important result of this kind of work is that no 

 embryonic growth-process so far investigated turns out to have a 

 temperature characteristic of 16,000, which is the typical one for 

 oxidations. In this connection the paper of Loeb & Wasteneys in 

 191 1 is interesting; it was entitled: "Are oxidation processes the 

 independent variables in life phenomena?" It occurred to them to 



