SECT. 12] CYCLOSES, PHOSPHORUS, SULPHUR 1211 



responds in an interesting way with tlie data of Plimmer & Scott, 

 for it looks as if the daily accretion of lipoid phosphorus in the embryo 

 rises until a point at which great quantities of the lipoid of the yolk 

 begin to be decomposed, and then falls off. Cahn thought that all 

 the constituents of the embryo would show peaks on the daily in- 

 crement curves, but, as may be seen from many of the graphs in 

 this book, in actual fact this is not the case. He interpreted the peaks 

 which do occur as being evidence of S-shaped curves of absolute 

 magnitude. But, as we have seen, not all such curves are S-shaped 

 in the time of the chick's development. Cahn finally calculated the 

 percentage growth-rate of the lipoid phosphorus, and found that it 

 followed the usual curves for percentage growth-rates of individual 

 substances (see Fig. 364). 



12-2. Tissue Phosphorus Coefficients 



The conception of tissue coefficients, or ratio values constant for a 

 given tissue for a given animal of a given age, first introduced by 

 Mayer & Schaeffer, is interesting in this connection. 



^^^ '^'''''- Total fatty acids 



Lipoid phosphorus' 



can be regarded roughly as a measure of the relati\ e amounts of lipoid 

 fatty acids and triglyceride fatty acids in the tissue. Mayer & Schaeffer 

 obtained the following figures in the course of their experiments, all 

 on the adult animal : , ^ . , . . , 



Total fatty acids/lipoid phosphorus 



Liver Kidney Lung Pancreas Muscle 



— 55 213 

 22 27 69 

 25 — 19 

 19 — 38 

 16 — 53 



— — 288 



Thus only two tissues, the liver of the guinea-pig and the lung of 

 the pigeon, had so little an amount of neutral fat that the ratio fell 

 below 17, though in four or five cases it fell to or below 20. On the 

 other hand, in certain cases the muscle showed an immense pre- 

 ponderance of neutral over lipoidal fatty acids. What happens in the 

 chick embryo during its development? Cahn calculated this ratio 

 from his data, with the result that it turned out to be well below the 

 very lowest of the adult values. In other words, the fatty acids of the 



