110 The Unity of the Organism 



us to the conclusion that in such experimental reproductions 

 there is a relation of dominance and subordination of parts. 

 The apical or head region develops independently of other 

 parts but controls or dominates their development, and in 

 general any level of the body dominates more posterior or 

 basal levels and is dominated by more anterior or apical 

 levels." '^ 



A really unique merit in Child's work is the fact that he 

 has given special attention to the connection of these axial 

 gradients manifesting themselves in various structural and 

 functional ways, with the fundamental metabolism of the 

 organism. Several methods of experimenting have been em- 

 ployed to this end, the one most frequently used being what 

 he calls the susceptibility or survival-time method. The es- 

 sence of this depends upon the fact, determined by many ob- 

 servers, "that a relation exists between the general meta- 

 bolic condition of organisms, or their parts, and their sus- 

 ceptibility to a very large number of substances which act 

 as poisons, i.e., which in one way or another make meta- 

 bolism impossible, and that difference in susceptibility may 

 be used with certain precautions and within certain limits as 

 a means of distinguishing differences in metabolic condition, 

 and more specifically, differences in metabolic rate." ^ 



The demonstration of metabolic gradients by this method 

 depends upon the fact that "death and disintegration of dif- 

 ferent parts of the body usually- follow a regular sequence," 

 this making it possible "to determine the time, not merely of 

 disintegration of the whole animal, but of the various re- 

 gions of the body." ^ 



Another way of showing difference in rate of metabolism 

 in different parts of the organism is by the use of the biom- 

 eter, an apparatus for estimating minute quantities of carbon 

 dioxide, recently devised by S. Tashiro in connection with 

 his important researches on carbon dioxide production in 

 nerves. By these methods it is shown, pointing to a single 



