488 MINNA E. JEWELL 



nearly the normal rate up to a certain point, and was then dis- 

 continued abruptly. Other experiments using H3PO4 gave 

 similar characteristic results. 



During the experiment a few tadpoles were transferred to 

 neutral distilled water to see whether normal regeneration could 

 take place after the initial stunting. Their subsequent regener- 

 ation is, of course, not added in with that of the other tadpoles 

 of the group in determining the average per cent of regeneration. 

 Tadpoles transferred during the first days of the experiment 

 underwent more regeneration than those left in the acids, but 

 their regeneration was far below normal. At the close of the 

 experiment all survivors were transferred to distilled water, but 

 none of them underwent further regeneration, showing that the 

 effect of acids is not merely a retardation, but a permanent 

 inhibition to regeneration. 



The curves in figure 19 represent the time required to regen- 

 erate 22.5 per cent of the amount removed in HNO3, and 25 

 per cent of the amount removed in HBr, H2SO4, and H3PO4. 

 The dotted line represents the actual experimental data, the 

 solid line the theoretical curve. Except in the case of H3PO4, 

 these lines coincide very closely. 



Figures 14, 16, and 18 are curves giving the time necessary to 

 complete the regeneration of various per cents of the amounts 

 removed in H2SO4, HBr, and HNO3, respectively. A comparison 

 of these with the curves for the regeneration in bases of various 

 per cents of the amounts removed shows that although in one 

 case (fig. 11) the regeneration in higher concentrations is irregular, 

 in general the curves are similar. In any given series all of the 

 curves of regeneration — which represent different stages in the 

 regeneration of the same animals — are roughly confocal. This 

 means that while the rate of regeneration at different stages is 

 different, regeneration progressing more slowly as it nears com- 

 pletion, the per cent of retardation due to acids or bases as 

 compared to normal regeneration is the same for all stages, or 

 that for each concentration the relative velocities for the different 

 stages are practically the same. In other words, if the times 

 required by tadpoles in any given concentration of an acid or 



