988 ENERGETICS AND ENERGY-SOURCES [pt. iii 



third week of incubation, there was no doubt about it. In 1925 I 

 pointed out that, although fat was the predominating energy-source 

 in the chick embryo, it could certainly not be the only one, for many 

 arguments indicated carbohydrate and protein as the energy sources 

 of the initial stages. 



1 . In the first 8 days of incubation there is a striking fall in the 

 amount of free glucose. The curves of Sato; Idzumi; By waters; and 

 Tomita, all show a rapid fall from about 0-4 gm. per cent, to o- 1 or less. 



2. Simultaneously with this disappearance of free glucose, the 

 lactic acid in the egg, which has previously been low, reaches a 

 peak and immediately afterwards descends to its previous level 

 (Tomita). From an initial level of 0-02 mgm. per cent, it attains on 

 the 5th day a maximum of 0-13 mgm. per cent., and regains its 

 original value about the 14th day. That it was intimately connected 

 with glucose metabolism he proved by injecting glucose, and ob- 

 serving an increase of lactic acid. 



3. When the figures of Bohr & Hasselbalch were examined (Fig. 

 144, p. 703), it was seen that, although the respiratory quotient 

 during the last two weeks of incubation is 0-73, in the earlier stages 

 it is nearly as high as unity^. 



4. The disappearance of glycogen in very early stages of develop- 

 ment has been investigated by Lewis and Konopacki. The former 

 grew tissue cultures of cells from very young chick embryos, and 

 could never find glycogen present in them after the first 50 hours 

 of development. Konopacki, working on the frog, obtained exactly 

 similar results. He found that after fertilisation and the formation 

 of the perivitelline space the glycogen greatly diminished in quantity 

 and remained very low until the neurula stage was reached, after 

 which the glycogen rose again. Similar results have recently been 

 reported by Vastarini-Cresi. All these workers made use of histo- 

 chemical methods. 



5. We saw evidence pointing in the same direction in the work 

 of Warburg, Posener & Negelein. They found a very marked pre- 

 ferential consumption of carbohydrate on the part of 3-5 day chicks' 

 tissue. The production of ammonia when the tissue was suspended 

 in bicarbonate Ringer in vitro was at once suppressed, if sugar was 

 provided for it. Negelein also found that the power of glycolysis is 

 very high in early development, and lower in the adult condition, 



^ And Dickens & Simer found quotients of unity for 5th day chick embryos in vitro. 



