SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



767 



early stages. Negelein's conclusion was that in the best conditions 

 there was practically no O.G.R., a finding which agreed very well 

 with the previous results of Warburg, Posener & Negelein on the 

 chick embryo. 



In 1927 Warburg collected together the data which had accumu- 

 lated for various tissues, with the object of proposing another entity, 

 the fermentation excess, or U., which he defined as equal to N.G.R. 

 — 2 R.R. Previously the comparison of tissues on the basis of their 

 O.G.R. had been difficult because of the high suscepdbility of the 

 reaction on which it depended; thus rat embryos in Ringer had 

 a considerable O.G.R. but in 

 serum only a very small one, 

 while in amniotic fluid they had 

 none at all. He therefore sug- 

 gested that it would be best not 

 to measure the O.G.R. directly, 

 but to calculate it from theo- 

 retical grounds. U. would be o 

 when the N.G.R. equalled 

 double the R.R., and negative 

 or positive if it was lower or 

 higher than double the R.R. In 

 the latter case, the oxidation mechanisms would be inferior in 

 efficiency to the glycolytic mechanisms and vice versa. Values for U. 

 are given in Table 9 1 . 



Other workers continued the investigations in the matter of em- 

 bryonic tissues. Krebs discovered the interesting fact that the adult 

 bird retina had a metabolism almost entirely composed of glycolysis, 

 with an almost unmeasurable respiration. His figures are shown in 

 Table 91. At the same time he found that the embryonic retina had 

 not so extreme a type of metabolism, having an O.G.R. of 33, 

 unlike the value of 133 for the adult. The construction of a curve 

 relating avian retina N.G.R. to age was undertaken by Tamiya, 

 whose graph is shown in Fig. 171. Beginning on the 8th day of 

 development at about 35, it rose steadily during incubation to reach 

 45 at the 15th day and 85 at hatching, after which it continued to 

 rise during postnatal life, until the adult value of 130 was reached. 

 Some observations seemed to show that in old age it declined again, 

 and was 90 at 4 years old. This result implied that just before 



Bebrijtungsfag 

 Fig. 171. 



