II50 THE METABOLISM OF NUCLEIN AND [pt. iii 



used White Leghorn embryos. As Fig. 347 shows^ the ratio, far 

 from being, as Targonski thought, a constant, changes very markedly. 

 Attention may first be concentrated on the curve obtained from 

 LeBreton & Schaeffer's data, i.e. the curve for embryo alone, the 

 membranes not being included. It begins at a very high value but 

 immediately descends to reach a minimum on the 1 1 th day, or, in 

 other words, a condition when the excreted purine — the uric acid — 

 somewhat exceeds the architecturally utilised purine. This minimum 

 precisely corresponds, as is 

 shown by the vertical line on 

 the graph, with the point of 

 maximum intensity of uric 

 acid production, which has 

 been already described, and 

 which is pictured in Fig. 323. 

 Later, Targonski's ratio rises 

 again, and then falls slightly, 

 although the uric acid excre- 

 tion always exceeds the laying- 

 up of purines in the cells. If 

 now the Fridericia curve is 

 considered, it will be seen that the ratio does not dip below the 

 unity line till the i8th day, which shows that, if the purines in the 

 membranes are taken into consideration, then the anabolic purines 

 rather exceed the cataboHc purine during most of development. The 

 first trough is present, although shifted some 2 or 3 days forward, but 

 the time of the subsequent peak is little changed. In short, Tar- 

 gonski's ratio varies during development with the intensity of protein 

 metabolism, as we should expect from the fact that the main end- 

 product of protein metabolism in the bird is a purine ring. 



10-2. The Nucleoplasmatic Ratio 



This expression was originally introduced by R. Hertwig, who in 

 1 903 suggested that there was a definite relation between the mass 

 of the nucleus and the mass of the cytoplasm. "The diminution of 

 the nuclear mass seems, as Boveri has shown, to bring with it a 

 diminution in cell size; the augmentation of the nuclear mass, 

 according to Gerassimov, leads to augmentation of cell-size." The 

 relation between the two was rapidly taken up by morphologists, 



Fig. 347- 



