914 



GENERAL METABOLISM 



[PT. Ill 



gms mfims 2 Day3-»5 



Fig. 244. 



The carbohydrate, protein, fat succession seen in these constitution 

 curves explains Murray's finding that the calorific value of the 

 embryonic tissue increases with age (see p. 947). Before leaving 

 Table 108, some interesting facts which emerge from the values 

 of the last three columns may 

 be briefly mentioned. Col. 13 

 gives the inorganic material in 

 the embryo in grams per cent, 

 taken from Murray, and to- 

 gether with Cols. 3, 6 and 12, 

 which represent the carbo- 

 hydrate, protein, and fat, it 

 ought to add up to nearly the 

 whole of the dry weight as ex- 

 perimentally measured. Actu- 

 ally, as Cols. 14 and 15 show, 

 it only adds up to about 90 per 

 cent., leaving 10 per cent, on an average for all the other substances 

 associated with life, lipoids, sterols, cycloses, pigments, waxes, etc. It 

 is interesting to see that this residual value declines steadily during de- 

 velopment, as if in the earlier 

 stages there were a higher per- 

 centage of substances not in- 

 cluded under the heads : carbo- 

 hydrate, protein, fat, ash. Of 

 course, estimation errors will 

 be included in the residual 

 value, and these will usually 

 lead to slight losses in the 

 substance estimated. When 

 accurate figures become avail- 

 able for the amount of lecithin 

 and cholesterol in the embryo, 

 for instance, it will be interest- 

 ing to begin the compilation of a balance-sheet of the residuum. 



Whether the curves for percentage constitution in the chick embryo 

 will be found to resemble those for other embryos we cannot as yet 

 tell. For the mammalian embryo, however, a certain number of 

 figures are available, though they in no way approach in thoroughness 



lCamerer-& 

 Sdldner- 



Klose 



■ Fat 

 0) Ash 

 -V Protein/ 

 sAsh 



o Protein JFehlIng 

 • Fat 



DProte;n|Mi 

 a Ash 



Months 

 lan Embryo Constitution 



Fig. 245. 



