. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 282 ADVENTURES IX RADIOISOTOPE RESEARCH inorganic P of very high activity is piesent ahnost at once after injecting the active sodium phosphate. The non phosphatide P of the yolk is partly inor- ganic P which gets into the yolk in the early stage of the experiment when its specific activity is very high; we mvist therefore consider the lecithin P and not the non- lecithin or total P content as a proper measure of the growth of the A oik. From the fact that the lecithin P of the 30—100 mgm yolks became active only to a v
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 282 ADVENTURES IX RADIOISOTOPE RESEARCH inorganic P of very high activity is piesent ahnost at once after injecting the active sodium phosphate. The non phosphatide P of the yolk is partly inor- ganic P which gets into the yolk in the early stage of the experiment when its specific activity is very high; we mvist therefore consider the lecithin P and not the non- lecithin or total P content as a proper measure of the growth of the A oik. From the fact that the lecithin P of the 30—100 mgm yolks became active only to a very slight degree we must conclude for example that they had hardly grown within tlK> last 28 hours. When discussing the labelled let-ithin P (phospha- tide P) present in blood and in some of the organs we shall find definite evidence that the yolk lecithin is dra^^^l from the plasma lecithin. It is of interest to remark that the ratio of the total active leci- thin content of small yolks, such as would require 10 daj's or more to attain completion, is a quanti- tative measure of their relative growth since the administration of the labelled P. When, however, comparing the lecithin P activity of a small yolk which increases its weight in the course of a da^- only to a slight extent with that of a large yolk growing at a rate of few gm per day the ratio of the total activities will not always be a correct measuie of the growth since the administration of the la- belled P. It may happen (comp. Fig. 2) that the giowth of yolk per hour is larger at the end than in the beginning of the experiment the latter process determining thus to a larger extent the total growth within the time of experiment. From which it follows, that if at the beginning of the experiment the specific activity of blood lecithin happens to V)e greater than at the end, we underestimate tlie growth of the large yoUc. It is, however, the determination of the slow rate of giowth of the small and tiny yolks, o
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