982 ENERGETICS AND ENERGY-SOURCES [pt. iii 



This is perfectly satisfactory so long as we only consider complete 

 combustions to carbon dioxide and water. Rapldne, however, 

 pointed out that the developing organism may have at its disposal 

 other sources of energy, for endothermic reactions are known to 

 occur in vivo, which raise the chemical potential of their products. 

 Confusion arose here owing to the fact that some workers used 

 the term "energy sources" to apply to the solids burned to give the 

 heat lost from the egg, while others used it to apply only to those 

 reactions, whatever they may be, which gave the energy of organisa- 

 tion, or O.E. Bohr & Hasselbalch showed finally that of the total 

 solid lost not more than 4 per cent, can participate in the O.E., but 

 when we take into account the energy not furnished by complete com- 

 bustions it is legitimate to suppose that a larger proportion of the 

 total energy turnover may be used for O.E. We cannot expect to 

 find this, of course, by bomb calorimetry, for the organisation is 

 destroyed by drying. Rapkine focused attention upon coupled and 

 spontaneous endothermic reactions, and considered that their existence 

 in the embryo explained inter alia ( i) the atypical respiratory quotients 

 which he had himself observed in echinoderm eggs (see p. 648), 

 (2) the low calorific quotients of Meyerhof (see p. 651), (3) the 

 initial heat absorption in Bohr & Hasselbalch's measurements (see 

 p. 704), and (4) the synthesis of fatty substances which proceeds in 

 many eggs. Applying these ideas to the efficiency formula, Rapkine 

 suggested that the numerator U' (calories in unit weight of finished 

 embryo) should be replaced by U' minus the energy contained in an 

 exactly equivalent weight of original raw material. This would 

 represent the elevation of calorific value which has gone on during 

 development : ^ r, _ 



U-iUn+Uj,)' 



It can be seen at once that this will give an efficiency of a very 

 low order, but not altogether comparable with those which have 

 already been discussed, such as the A.E.E. and the R.E.E. For what 

 they measure is the relation between the energy in the substance 

 stored in the embryo or transformed into its tissues, on the one hand, 

 and the energy absorbed by the embryo from the raw materials, on 

 the other hand, either allowing for the basal metabolism or not 

 allowing for it. Rapkine's efficiency coefficient, on the contrary, 

 measures the relation between the energy furnished to the embryo 

 from coupled reactions, etc. (energy which would have been dissi- 



