206 



COMPARATIVE PHYSIOLOGY 



above criticism ; the new data are decidedly confirmatory of 

 the main contentions of Child's work * 



Shearer first studied (a) portions of the living chick embryo 

 from the anterior and posterior ends of the blastodisc during 

 the first ten days of incubation ; (b) pigments from the anterior 

 and posterior extremities of the earthworm. In the first case 

 the oxygen consumption was measured by Barcroft's differential 

 m.anometer. In the second case Haldane's apparatus was 



10 



Days 4 5 6 7 8 9 



Fig. 44. — Oxygen consumption of chick embryos (Shearer). 



employed. In both sets of experiments the tissue used was 

 incinerated and estimated for protein content by Kjeldahl's 

 method. Thus all values of oxygen were expressed in absolute 

 units by reference to an equivalent amount of NH3 liberated 

 in the Kjeldahl determination at the end of the experiment. 

 The results of the experiments on chick embryos are repre- 

 sented graphically on Fig. 44. Here the point to notice is 

 that the gradient of the oxygen consumption curve for the head 

 and tail portions become identical at the seventh day, when 



* [Note by the Editor, Sept., 1925.] Later, as yet unpublished, work 

 has somewhat modified these conclusions, Dr. Shearer informs me. 



