930 GENERAL METABOLISM [pt. iii 



When one shows that a certain amount of one kind of building-stone 

 has entered the embryo and the other shows that it is not to be found 

 there in the form in which it went in, the inference may be drawn 

 that it has been changed into some other material of architectural 

 or energetical value. Now not all the fat entering the embryo 

 between the 8th and 1 1 th days appears there immediately afterwards 

 as fat. One cannot help being reminded of the coincident transforma- 

 tion of fat into carbohydrate, which will be discussed below in 

 Section 8-4. At that time some 40 mgm. of carbohydrate rather 

 suddenly appear from somewhere, and at the same time there is a 

 quantity of missing fat of about the same order. That these transforma- 

 tions appear to take place in the extra-embryonic part of the egg is 

 no objection to the view that they really take place in the embryo, for 

 the circulation in the egg is fairly efficient at that time, and could 

 readily bring the reactants in this change to and from the embryo. 

 In fact, just as we are accustomed to assume that absorption must 

 precede combustion, so it would be logical to assume that absorption 

 must precede fat-carbohydrate transference. There would then be no 

 reason why the products of this reaction should remain in the embryo. 

 Although the absolute amount of substance thus transformed is small 

 enough yet relatively to the size and constitution of the embryo at 

 the time when it takes place, it would account for the peak in the 

 absorption curve. If these arguments are sound, then we must 

 picture an increased passage of fat into the embryo towards the mid- 

 point of development, having for its goal the formation of some new 

 carbohydrate. This will then return to the yolk, and in a short time 

 give rise partly to glycogen in the transitory liver and partly to some 

 other form of combined sugar. 



It will have been noticed that, though the peak in the protein 

 constitution curve corrected for feather protein shows some corre- 

 spondence with the protein combustion curve (11 days : 8-5 days), 

 it would be rather more fitting when comparing the constitution 

 curve with the absorption curve to use the uncorrected values. When 

 this is done, there is revealed an exact correspondence ( 1 6 days : 1 5 

 days). 



The method of calculation which has proved so successful in com- 

 paring relative absorption intensities in the case of the chick embryo 

 unfortunately cannot be applied to mammals, for we do not know, 

 and at present have no means of knowing, what the active mass of 



