948 ENERGETICS AND ENERGY-SOURCES [pt. iii 



data. Tangl's first paper dealt with the avian egg, and he defined 

 his aim as the attempt to see how much energy was utiHsed during 

 development, in what manner the process went on, and what were 

 the sources of it. He was profoundly impressed by the difficulty and 

 the fascination of the problem of "work of development", the 

 problem of relating the morphological and structural coming-into- 

 being with physico-chemical work done. It was not possible, he 

 felt, that living animals should acquire ontogenetically their shape 

 and form, without having to pay a fee, perhaps a heavy one, to 

 entropy. Obviously this question is one of some difficulty, and a 

 good deal depends on definitions, in which respect Tangl and his 

 school were not altogether happy. "Die Menge der wahrend der 

 Entwicklung des Embryos umgewandten chemischen Energie, 

 nenne ich Entwicklungsarbeit", said Tangl. Thus the first figures 

 he obtained (on the egg of the starling) 



cals. 

 Undeveloped egg ... 3067 



Finished embryo ... 2312 



Entwicklungsarbeit 755 



showed the method he intended to adopt. In calling the total amount 

 of energy not used for storage in the embryo "Entwicklungsarbeit", 

 Tangl was confusing two things which it is important to keep 

 separate, (i) the amount of energy used by the formed cells of 

 the embryo during development for combustion processes, and dis- 

 appearing as heat, and (2) the amount of energy, if any, which passes 

 into the embryo in the form of food from the yolk and white, and 

 which is yet not recoverable from the dried material by the bomb 

 calorimeter. This second fraction has more right to be called "Ent- 

 wicklungsarbeit" than the first one, for as soon as any new cell is 

 formed it begins an oxidative metabolism of its own. Undeniably 

 this is work done during development, but not a true "Entwicklungs- 

 arbeit", the energy of which would have to be put down on the 

 balance sheet of ingoings and outgoings as missing, i.e. in some way 

 bound up with the structure. Exactly how this could take place has 

 been the theme of several speculations; thus some have suggested that 

 energy would be required to maintain certain orientations of mole- 

 cules at intracellular surfaces, and doubtless the form of the animal 

 is the outward and visible sign of such inward steady states, but 

 these postulated processes have never been demonstrated. There is 



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