Vol. LII January, 1927 No. I 



BIOLOGICAL BULLETIN 



THE METABOLIC GRADIENTS OE VERTEBRATE 

 EMBRYOS. III. THE CHICK. 



LIBBIE H. HVMAN. 

 HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO. 



The aim of these investigations was stated in the preceding 

 papers of this series (Hyman, '21, '26) and repetition here seems 

 unnecessary. Briefly it is hoped that the facts presented in 

 these papers may serve as a basis for the interpretation of normal 

 and teratological development. The method consists in ob- 

 serving the time of death of different regions of the embryo in 

 lethal solutions. The time elapsing between exposure to the 

 solution and death is taken as roughly proportional to metabolic 

 rate and the method thus serves to reveal differences in rate of 

 activity in different parts of the embryo. The grounds on which 

 this interpretion is based are briefly presented in the preceding 

 paper of this series (Hyman, '26) and have been fully discussed 

 in various publications from this laboratory (e.g., Child, '13; 

 Hyman, '20). 



The main facts about the gradients of the chick embryo have 

 been known to me for about ten years. The gradients were 

 worked out in detail in 1920 but the data upon the heart were not 

 as complete as desired and publication has been delayed on this 

 account. Every spring and fall since 1923 some time has been 

 spent in s'tudying the disintegration of the heart, a structure 

 not very amenable to investigation by the susceptibility method. 

 Much time and material must be wasted to obtain certain 

 developmental stages which endure but an hour or two. I have 

 finally, however, beeri^able to bring the study to a reasonably 

 satisfactory conclusion. 



