17. 

 to the CO, produced by the tadpoles the distilled water became acid and the 

 NaOH solution less basic. However, it was no longer neutralized. The retarda- 

 tion to regeneration (Fig. 17) is very marked in 25 o.c. NaOH per liter while 

 50 o.c. per liter proved fatal in two d.^ye. 



These results are in accord with the suggestion of Loeb (1904) 

 that the beneficial effect of the addition of a base is due, not to the presence 

 of hydrozyl ions, but to the neutralization of acids produced by the animal, and 

 show that a P H between 3 and 9 is markedly detrimental. 



Regeneration Ir Acids 



As the previous experiments show, neutrality is more favorable 

 for regeneration in talpoles than bacisity. Is the same thing true of acidity? 

 A complete series from acids, almost certain to H«rw detrimental effects to bases 



•n to be harmful, was formed by using 25, 20, 15, 10 and 5 c.c. of 0.01 mol. 

 H 3 P0 4 and 5, 10, 12.5, 15, 17.5 and 20 c.C. of 0.01 H NaOH made up to 200 c.e. 

 with 5 o.c. 0.01 mol. neutral Na 2 HPO| ^ KH 2 P0 4 mixture as a neutral control as 

 well as the usual distilled water controls. The solutions were changed daily. 

 It was hoped in this ray to locate approximately the optimum hydrogen ion con- 

 centration for regeneration. 



The results are given in tables 14 and 14a (Exp. 8). The results 

 for H«P0^ (table 14) are not very conclusive, as the rate of regeneration 

 (Fig. 18) is about the same for all concentrations which are not fatal. The 



total amount regenerated is, however, greater in the three controls. The 

 neutral phosphate control lies midway between the two distilled water oontrols, 



shoring that the presence of Na, K and P0 4 ions in the small amount employed is 

 neither beneficial nor detrimental. 



The results of the NaOH series (table 14a) are definite, showing 

 a progressive decrease in both the rate of regeneration and the amount regener- 

 ated, as the concentration of base is increased. While the curve of growth 



