ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 



665 



since it was observed that thyroxin-treated tadpoles failed to feed. 

 Figure 1 illustrates the marked alterations induced in Rana cates- 

 biana exposed to thyroxin for 11 da vs. The rate at which the tail 

 was resorbed is charted in Fig. 2. 



Fig. 1. Resting tadpole Rana caicshiana; abo\e, tadpole after 9 davs' treat- 

 ment with thyroxin. 



The most dramatic change in composition in the tissues of meta- 

 morphosing animals is a consideral^le loss of water, about 50 per 

 cent in the fin and 25 per cent in the back skin (Table I) after 

 6 days' exposure to thyroxin. Collagen concentration, as well as free 

 proline and DNA (representing cell content), was proportionately 

 increased. Noncollagenous protein, on the other hand, showed 

 relatively little increase in concentration. Composition changes of 

 the whole tail fin, however, conformed closelv to the visible observa- 

 tion of tissue resorption. Total tail fin weight diminished by three- 

 fourths, with collagen and DNA falling approximately 50 per cent. 

 Free proline dropped to two-thirds of the control value. The non- 

 collagenous protein fraction* fell even lower, decreasing to one- 

 quarter of the original level. 



The loss in tissue water during metamorphosis is well known; the 

 literature was recentlv reviewed by Frieden ( 1961 ) . 



* Represented by the protein of the extract which does not precipitate with col- 

 lagen on dialysis against water. 



