SECT. 7] OF EMBRYONIC DEVELOPMENT 963 



We may now return to the distinction made above, namely, that 

 while no one could have taken exception to Tangl's ideas on "Ent- 

 wicklungsarbeit " if it had been defined as the amount of energy 

 disappearing in the solids combusted during a given amount of em- 

 bryonic architectural work, yet throughout Tangl's writings the im- 

 pression conveyed was that the " Entwicklungsarbeit " was the amount 

 of energy disappearing for a given amount of architectural work. 

 It is, of course, true to say that no embryonic growth, or any other 

 kind of vital process, can go on without a certain wastage, for living 

 machines are far from having an efficiency of 100 per cent., but there 

 is no reason for supposing that the energy lost by combustion in the 

 growing embryo is in any way quantitatively related to the actual 

 increase of differentiated structures. It would, in fact, have saved a 

 great deal of controversy if Tangl had expressed his results in terms 

 of efficiency, for that is their real significance. To say that it involves 

 a loss of 3100 cal. to build i gm. dry weight of silkworm, and that 

 it involves a loss of 3280 cal. to build i gm. dry weight of minnow 

 is simply to say that the work of storage which the fertilised egg-cell 

 has before it cannot be accomplished without a certain amount of 

 waste. In the case of the hen, the efficiency of storage is 62-9 per 

 cent., in the case of the silkworm it is 63-2 per cent., in the case of 

 the minnow it is 52-8 per cent., but this last value is certainly too 

 small. Roughly it can be said that the efficiency of energy storage 

 is in the neighbourhood of 66 per cent, in most of the cases known. 

 This is so because the average calorific value of formed living tissue 

 (average for whole body) is much the same. The important fact 

 about Table 121, then, is not that the absolute values for Ea. come 

 out so much aUke, because, after all, the absolute calorific values for 

 the tissues are alike, but that the relation between these is constant, 

 and, in fact, that embryonic development goes on, as far as ^ve can 

 tell, with a constant efficiency in different animals. 



But because Tangl apparently did not appreciate the real signi- 

 ficance of his figures he was misunderstood from the first. Ham- 

 marsten, in an edition of his text-book which appeared during the 

 publication of Tangl's series, showed that he did not understand 

 Tangl's point of view. Then Bohr & Hasselbalch, in their paper on 

 the heat production of the hen's Qgg, took over Tangl's expression 

 "Entwicklungsarbeit", but used it in a quite different sense, namely, 

 that of energy retained for organisation, or O.E. Bohr & Hasselbalch 



