964 ENERGETICS AND ENERGY-SOURCES [pt. iii 



felt that to speak of all the energy lost by the egg during its develop- 

 ment as "work of development" was obviously wrong, for to do so is 

 to assume that all the energy lost has been used for development proper 

 apart from the maintenance of life. The only real sense, argued Bohr 

 & Hasselbalch, in which the term " Entwicklungsarbeit " can be used, 

 is to denote that portion of energy, if any, retained by the organism 

 in the passage of fuel material into end-products. Krogh later sup- 

 ported this view. If there was any "cost of production" of embryo 

 from yolk and albumen, then direct and indirect calorimetry would 

 be expected to give different results. These considerations were among 

 those which led Bohr & Hasselbalch to determine the oxygen taken 

 in by the egg and the carbon dioxide and heat given out. As we have 

 already seen (see p. 704 and Fig. 145), the curves for observed and 

 calculated heat production were practically superimposable between 

 the 8th and the 19th days of incubation. There was no retention 

 of heat by the embryo, and therefore no true Ea., i.e. no O.E. 

 But this statement has to be qualified by the proviso that their 

 figures showed a discrepancy of 4 per cent., which might or might 

 not have been heat retained. 



These relationships are shown in Fig. 259. The original 87 Cal. 

 of chemical energy present in the hen's egg at the beginning of 

 incubation divides itself into 26 Cal. of unused yolk on the 21st day, 

 37 Cal. of embryonic tissues and 23 Cal. given off as heat from com- 

 bustion. These form 30-4 per cent., 43-2 per cent., and 26-4 per cent, 

 respectively of the initial provision. Side by side with the column 

 showing the amount of energy which is contained in one hatching 

 chick, another column is placed showing the amount of energy which 

 would be present in a bottle containing all the compounds present 

 in the chick, in their precisely correct concentration, but in the state 

 of powders or liquids, i.e. entirely unorganised. It is evident that, 

 as we have not a complete analytical balance sheet of all the sub- 

 stances present in the embryo, still less of their calorific values, intra- 

 molecular constitution, degree of activation, etc., we cannot at present 

 measure the difference between these two columns, especially as 

 there is reason to believe that it would be very small. However, a 

 portion is marked off at the top of the right-hand column, and 

 labelled O.E. It is to be supposed that Bohr & Hasselbalch's 4 per 

 cent., if it is not simply due to errors of technique, would take its 

 place as part of the O.E. It will be evident that Tangl's work tells 

 us nothing at all about the O.E., or, as we defined it before, the 



