934 GENERAL METABOLISM [pt. m 



especially the mesonephros — but not in the yolk, the amniotic liquid, 

 the amniotic membrane or the lumen of the intestine, although if the 

 egg was not opened for a week or so after injection, the dye would 

 appear in the second group of structures also. The fact that trypan 

 blue, although present in the egg-white at a time when a marked 

 absorption of water is going on by the yolk, does not enter the yolk, 

 throws a light on the properties of the vitelline vessels. Similar work 

 was done by Latta & Busby^. Zaretzki also noted that methy- 

 lene blue does not enter the yolk from the albumen. After the 

 opening of the sero-amniotic duct about the 12th or 13th day of 

 incubation, the amniotic liquid includes flakes of the protein from 

 the albumen-sac, stained blue, and these enter the chick's intestine. 

 Wislocki's failure to obtain entry of the dye into the egg from the 

 air-space must have been due to the use of too small injections, for 

 Hanan found that dye appears in the mesonephros about i^ hours 

 after injection into the air-chamber. 



6-10. Storage and Combustion : the Plastic Efficiency Coefficient 



Absorption of raw materials for embryonic growth can be con- 

 sidered in several ways. Related to the embryonic substance already 

 formed, it gives absorption rate; related to the embryonic substance 

 already formed and to the raw material remaining, it gives absorp- 

 tion-intensity; related to the amount of substance being simultaneously 

 combusted, it gives storage efficiency. We may now consider the 

 last-named of these entities. The substrates of the absorption process 

 divide perforce into two parts, one of which is stored and the other 

 combusted as a source of energy. 



The degree of efficiency with which the transference of yolk and 

 albumen into flesh and blood is effected may most conveniently be 

 expressed by an efficiency coefficient. This corresponds to the 

 " Rendement materiel " of Henri, the "Coefficient d'utihsation" of 

 Terroine & Wurmser, the " Coefficient economique " ofPfeffer, and 

 the "Plastic equivalent" of Waterman. The best name for it would 

 seem to be "Plastic efficiency coefficient" (P.E.C. for short), for 

 this shows that it has nothing to do with energy content or ex- 

 penditure, and explains that it is a measure of efficiency of transfer 

 of matter. It may be described as the ratio: 



Dry weight of embryo/Dry weight of absorbed solid, 



1 Fazzari, too, has studied the absorption of iodine after injection into the yolk. 



