208 J. S. NICHOLAS 



On the basis of his own work Brachet ('44) concludes that the nu- 

 cleus is the center of protein synthesis, in contrast to Caspersson ('41), 

 who concludes that the nucleolus is the initiator of the reaction and that 

 the proteins are synthesized in the cytoplasm while the nucleolus acts as 

 the center for histones and the nucleus for the ribonucleic acid. Brachet's 

 studies on the roles of thymonucleic, ribonucleic, and desoxyribonucleic 

 acids in cell metabolism tend to strengthen his viewpoint concerning the 

 character and action of these specific substances. 



While there have been numerous studies of oxidation rate in the de- 

 veloping embryo, there has been little correlation of the facts so derived 

 with the organizational picture. Boell's findings indicate that carbo- 

 hydrate metabolism rather than respiration is the major significant 

 factor. There have, however, been definite correlations between the de- 

 velopment of definite chemical entities with both morphological and 

 functional development, and a few examples of this phase of the work 

 will be given. Sawyer ('43) has shown the rate and amount of develop- 

 ment of cholinesterase and has correlated this with the onset of the em- 

 bryonic nerve-muscle reaction. 



The enzyme remains constant in quantity during the early stages, de- 

 riving its activity in causing nerve-muscle reaction by the concentration 

 of practically the total amount of cholinesterase in the nervous and myo- 

 tomic structures. The increase in content begins with stage 36, when the 

 behavior pattern demonstrates the S-flexure, after which the enzyme 

 grows in quantity such that it can be represented as a sigmoid curve up 

 to the feeling stage. By placing Amblystoma in solutions of prostigmine 

 and eserine, Sawyer was able to change the rate and amount of the 

 cholinesterase development. In a further study Sawyer ('43) has studied 

 the cholinesterase concentration in the nervous system and in the total 

 animal, showing the increase in concentration during the period of func- 

 tional organization. 



The cholinesterase activity reaches its peak in Amblystoma about fifty 

 days after fertilization in both nervous system and muscle and then de- 

 clines in both, but more drastically in muscle than in nerve. The adult 

 activity is represented by the same concentration of cholinesterase that 

 is found in some of the pre-feeding stages. When the spinal cord of the 

 embryo is removed so that the muscles develop in denervated condition, 

 the curve of the development of cholinesterase is much lower in the 

 muscle than in the innervated muscle. There is, however, a residuum 

 amounting to 31 % of the normal in late swimming stages, showing that 



