SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 753 



They may be found discussed in the books of Terroine & Zunz and 

 of Lipschiitz. LeBreton & Schaeffer, however, in their work on the 

 nucleoproteins of the chick embryo, were led to regard the para- 

 plasmatic substances as mainly proteins from the fact that the nucleo- 

 plasmic ratio, chemically determined, fell with age in the chick 

 embryo. Other proteins were therefore rising, and the active mass, 

 they thought, could be represented by (though of course it was not 

 regarded as identical with) the nucleic acid nitrogen as percentage 

 of the total nitrogen. Some typical figures for the chick embryo were: 



Chemical nucleoplasmic ratio 

 Days of (Nucleoprotein nitrogen x ioo)/(Total 



development nitrogen - nucleoprotein nitrogen) 



8 IO-7 



6-65 



4-9 



35 



and naturally LeBreton & Schaeffer emphasised the similarity 

 between the fall in nucleoplasmic ratio and the fall in metabolic 

 rate. Cahn, working under their influence, found in a study of 

 atrophy in muscle during starvation that the nucleoplasmic ratio 

 changed. Normal muscle contained for 100 gm. of total protein 

 0-684 gn^' of nucleic acid, but atrophied muscle 0-961 gm. of nucleic 

 acid for every 100 gm. of total protein. This was regarded as support 

 for the theory of paraplasmatic substances, but the interpretation 

 has been much criticised by Terroine. Terroine & Ritter carried 

 out experiments which were the converse of those of LeBreton and 

 Schaeffer on nucleic acid, for, instead of taking the same organism 

 at different ages (and therefore sizes), they took different organisms 

 of various sizes. Their results worked out thus : 



Purine nitrogen in grams per 

 100 gm. wet weight of tissue 



They concluded that these animals contained almost exactly the 

 same amounts of nucleic acid in their cells, and that there was 



