676 



C. M. LAPIERE AND J. GROSS 



10^ 



CONTROL 



THYROXIN Rx 



30 



Fig. 8. 



20 25 30 5 10 15 



HOURS AFTER PROLINE-h' 

 Specific activity of the three coHagen fractions isolated from tail fin 



thyroxin-treated animals along with 43 per cent diminution of the 

 total amount of this fraction (Table II) suggests either diminished 

 synthesis, accelerated breakdown, or increased conversion to the 

 insoluble pool. Diminished net synthesis but not rate would be ex- 

 pected because of the loss in total tissue dry weight, as discussed 

 earlier. Since the total counts in the insoluble fraction are un- 

 changed, there may also be an increased conversion rate. 



On examination of the back skin data ( Figs. 9 and 10 ) , it appears 

 that in the neutral-extractable fractions, total and specific activities 

 we:e practically identical for control and treated groups. Specific 

 activity of the insoluble fraction, though somewhat elevated above 

 that of the control, did not approach the differences seen in the tail 

 fin. The specific activity of the neutral-extracted fraction always 

 remained considerablv greater than that of the insoluble component 

 although the total radioactivity was about the same for both. There 



