RATE OF RENEWAL OF THE FISH SKELETOX 213 



lish without its ogfjs was found to be 17.78 mgm, or 1.17 per cent, while 

 Ihe corresponding figures for the eggs were 2.7 and 0.29. 



Fish No. 16 hada weight of 1.07 gm including its eggs, which made up 

 40 per cent of the total weight. TJver and heart were strongly degenera- 

 ted, the liver weighing only a few milligrams. The duration of the experi- 

 ment was 16 days, the activity of the eggs amounting to 12.8 per cent 

 of the total activity. In the above case (No. 16 B), the corresponding 

 ratio was 18.3. Thus, after the lapse of 16 days, only about 2/^ of the egg 

 P was found to be incorporated in the eggs in the course of the experi- 

 ment, while in experiment No. 16 B., after the lapse of 23 days, almosi 

 the whole P content of the eggs was deposited (through growth or 

 renewal) in the course of the experiment. 



In experiment No. 16 A., the percentage of P taken up in the course 

 of the experiment from the water was found to be 1/3.9 • 10'* of the amount 

 present, corresponding to 2.2-10"'^ y. 



In experiment No. 16 B, 1/2.2-10* of the water P was taken up by 

 lhe fish amounting to 4.4 -10"^ y. 



DISCUSSION 



The average value for the degree of renewal of the fish skeleton in the 

 course of 22 days was found to be 2.5 — 5 per cent, the lower value being 

 the more probable. This means that, while 2.5 — 5 per cent of the skeleton 

 were renewed once or several times — a part of this percentage was 

 presumably renewed frequently — at least 95 per cent of the skeleton 

 remained entirely unchanged. When arriving at this conclusion, we 

 assumed that no additional growth of the skeleton took place in the 

 course of the experiment. As such additional growth would take place 

 from a labelled plasma, all newly formed skeleton might be expected 

 to be labelled, and what we interpreted as a renewal of the skeleton 

 might in such a case be due to additional bone formation in the course 

 of the experiment. We could not find any evidence for a growth of the 

 skeleton or a growth of the fish taking place in the course of the experi- 

 ment. It is very difficult, however, to exclude the possibility of an in- 

 crease in the mineral constituents of the skeleton by a few percent. The 

 above mentioned 95 per cent therefore have to be considered a lower 

 limit for the part of the skeleton remaining unchanged after three weeks. 

 In the case of the fully grown rabbit, about 10 per cent of the skeleton 

 were found to be renewed in the course of only 9 days (II eves Y et al. 

 1940). The great difference in the renewal rate of the skeleton of the 

 rabbit and that of the fish is presumably due to the great difference 

 in the body temperature. The renewal of the skeleton is partly a "physi- 

 cal" replacement process between the phosphate of the uppermost 



