PROBLEMS OF ORGANIZATION 2O9 



the nervous system is not entirely responsible for the organization of this 

 functional unit. 



The results of Sawyer ('43) have been checked by Boell and Shen 

 ('44) in their study of the cholinesterase content of induced neural 

 structures. 



The results of measuring the cholinesterase content of various tissues 

 in developing the embryos of Amblystoma punctatum indicate a signifi- 

 cant localization of cholinesterase in the nervous system in comparison 

 with the ectoderm at the period of development marked by the closing 

 of the neural folds. As differentiation of the nervous system proceeds, 

 the concentration of cholinesterase in neural tissue becomes progres- 

 sively greater. 



The cholinesterase activity of secondary or induced neural structures 

 produced by the action of implanted chorda mesoderm upon competent 

 ectoderm is of the same order of magnitude as that of the primary nerv- 

 ous tissues of the host and is much larger than that of ectoderm which 

 has not received the stimulus of the inductor. It appears then that the 

 phenomena of induction, in addition to causing the development of dis- 

 tinct morphological changes in the induced tissue, stimulates also the 

 latter to develop the biochemical machinery which is characteristic of 

 normal nervous tissue. They suggest that cholinesterase content of sec- 

 ondarily induced neural structures can be regarded as the measure of 

 their potential or incipient functional differentiation. 



Boell ('45), in his study of the correlation of respiration and the 

 presence of cytochrome oxidase, finds that the respiratory rate increases 

 steadily throughout development and varies exponentially with time, 

 although it seems impossible to correlate specific morphogenetic effects 

 with abrupt changes in velocity of oxygen uptake. The rate of respira- 

 tory increase is not constant and shows a distinct break at stage 30. The 

 evidence supports the conclusion that the rise in respiratory rate noted 

 during development is the result of growth of the embryo, i.e. the trans- 

 formation of the inert yolk into metabolically active material. The res- 

 piration of Amblystoma punctatum embryos is markedly susceptible to 

 cyanide throughout development, but is especially so in the later stages. 



As in the case of respiration, the cytochrome activity of Amblystoma 

 punctatum embryos increases steadily throughout the entire period of 

 development and apparently varies directly with increase in metabolically 

 active embryonic mass. Various lines of evidence suggest that respira- 

 tion is largely mediated by cytochrome oxidase throughout develop- 

 ment, but the absolute rate of oxygen uptake at any given stage is lim- 



