KATE OF RENEWAL OF I'UE FISH SKELETON' 21 1 



Gasterosteus aculcatus is a fish provided with a skin armour^ Tn several 

 cases, we investigalcMl Ihe ariiiour'. the cranium, and the vcniebra sepa- 

 ralely. 



EXTENT OF RENEWAL OF THE SKELETON 



The method ol' calculating^ the extent of renewal of the skeleton is 

 shown by the following example. 



Duration of the experiment = 16 days. Average temperature = 16.6'^. 

 Fresh weight of the fish = 1.49 gm. Weight of the fresh liver = 50 mgm. 



Free P content of the liver = 21 y. 



Total P content of the skeleton = 3.98 mgm. 



Activity of the skeleton P = 29.2 counts per minute. 



Activity of the free liver P = 8.8 counts per minute. 



Activity of 1 y skeleton P _ 0.00733 

 Activity of 1 y free liver P 0.418 



Activity of 1 }' skeleton P in percentage of the activity of 1 y liver P 1.8. 



The figure obtained is not strictly identical with the percentage of the 

 skeleton which, in the course of the experiment, is renew^ed, as we com- 

 pared the specific activity of the bone P at the end of the experiment 

 with the specific activity of the free liver P at the same date, while 

 we should have considered the average value of the specific activity 

 of the free liver P prevailing throughout the experiment. This magnitude 

 is not known, but cannot be less than V2 of the final value. Therefore, 

 we have to multiply, the result of 1.8 per cent arrived at by a figure 

 which is less and probably appreciably less, than 2 in order to arrive 

 at a correct renew^al percentage which, thus, amounts to 3 — 4 per (!ent 

 in the course of 16 days. This percentage of the skeleton w^as renewed 

 once or several times, while the remaining 96 — 97 per cent of the skeleton 

 remained unchanged. 



The fish was kept in 3 litresof sea-water to which 3.4 mgm of labelled 

 phosphate, corresponding to 0.73 mgm P and having an activity of 1 .6 • 10<^ 

 counts, were added (measured the same day as the activity of the liver 

 and that of the skeleton). Water and activity were daily renewed. 



1 y free liver P was found to contain part of the activity and. 



^ 4-106^ 



thus, from the free P extracted from the liver 2-10"'* -/ were sucli 

 which originate from the labelled phosphate added to the sea-water. 



The total free liver P contained part of the activitv added to 



1.8-10^ 



^ A detailed de.Sf'i'iption of ihe armour is given by F. Roth (1920). 

 14* 



