950 



ENERGETICS AND ENERGY-SOURCES [pt. iii 



O Ea 



© RE,, 

 ® SEa 



happened on incubation is shown in Fig. 257. The energy contained 

 in the tissues of the embryo increased steadily with its growth ; that 

 contained in the remainder of the egg equally steadily decreased, 

 but in addition there was, of course, a loss from the egg as a whole 

 due to the combustions. This loss appears on the graph as a shaded 

 area, the extent of which at the end of development represents the 

 Ea. and amounts to 16 Cal. This is more energy than is spent by the 

 starling embryo during its development, but the chick embryo is 

 larger than that of the starling. In order to have a common basis of 

 comparison, Tangl computed 

 the Ea. as related to i gm. of 

 embryo (wet weight), which 

 he called the "relative Ent- 

 wicklungsarbeit ' ' (hereafter 

 referred to as the R.Ea.), and 

 as related to i gm. of embryo 

 (dry weight), which he called 

 the "specifisches Entwick- 

 lungsarbeit" (hereafter re- 

 ferred to as the S.Ea.). When 

 these values were calculated 

 out for the chick, he obtained 

 the graph shown in Fig. 258. 

 The Ea., of course, rose during 

 development, for the quantity 

 of material burned on any 

 one day rose, but the R.Ea. 

 and the S.Ea. fell, as they 



were bound to do, owing to the declining metabolic rate. Tangl 

 introduced some corrections at this stage for the weight of the 

 membranes in the early stages, but, even after these had been made, 

 the R.Ea. and the S.Ea. were still much higher for the earlier than 

 for the later stages. In other words, more energy was dissipated 

 in forming i gm. of loth day embryo (wet or dry weight) than 

 in forming i gm. of 21st day embryo, a conclusion quite in harmony 

 with all that is known about the change in respiratory intensity 

 with age. 



Tangl compared the magnitude of R.Ea. in the chick embryo with 

 the " Erhaltungsarbeit " or basal metabolism of the adult hen; an 



The dotted lines sh^ 

 the figures corrected 

 for the membranes 



Days 



Fig. 258. 



