SECT. 3] 



AND ORGANISATION 



587 



case with Planarians) ". This view finds many supporters among those 

 famiHar with the Winkler method. 



Hyman and Child made an attempt to gauge the concentrations 

 of glutathione at the different levels of the stem of tubularians, 

 using a modification of the nitroprusside test, from which they 

 concluded that glutathione gradients were present. Such a statement, 



15 



en 



X 



O 



10- 



o 



Days 4 5 6 7 8 9 10 



Fig. 96. 



however, cannot be accepted in the absence of exact quantitative 

 data, especially considering the unspecific character of the nitro- 

 prusside test applied to an intact animal. 



Apart from these rather unsatisfactory researches, nothing has 

 been done by Child and his collaborators on the direct verification 

 of their theory. In spite of this, they carried over the conception 

 of metabolic gradients to the developing embryo without modification, 

 and the question naturally arises, to what extent were they justified in 

 doing so ? The position is, in a word, that it cannot yet be considered 

 as proved that gradients of metabolic rate exist, much less that they 

 accompany gradients of other entities, such as susceptibility and 



