IB. 

 of tadpoles In 5 c.c. lies above the controls, the hydrogen ion determinations 

 •ho* that this eolution is not only neutralised but becomes 9lightly acid within 

 twenty-four hour*, §mi it h is already bean shown (Exporlurant 7) that this sane 

 coneentr-.tio ; of base is distinctly harmful if tha voluwa is sufficient to 

 pravent its bein; noutralizsi. Fig. 20 gives the time necessary to regenerate 

 25, 3" and 35$ of the amount removed. 



The next series of experiments (9, 10, 11 ami 12) involving 

 124 tadpoles was made in order to compare the effects upon regeneration of 

 the various adds. Tha experiments were carried on in finger bowls containing 



200 c.c. of the solution. Four tadpoles were placed ia each dish and the 

 solutions were ohangad rilteraate days. The acids used were 0.01 !f HNO3, 

 HBr and H 2 S0 4 end 0.01 raol. H 3 K> 4# Tables 15, 16, 17 and 18 respectively 



give the results of the experiments. The tadpoles in tUo HKO3 series were 

 •lightly •waller than those in the H 2 504 and HgP0 4 series, those in HBr sere 

 somewhat larger* 



A comparison of the tables or figures (21, 22, 23 and 24) show 

 that In HKO3, H^r an! H2SO4 tie retardation of regeneration is gradual and 

 comparatively slight in concentrations up to 12.5 c.c. (.000625 H) . As the 

 concentrations rise above this, tha retardation to metabolism increases very 

 rapidly, the order of toxicity of the acids being HNO3, HBr, H 3 ?0 4 . This 

 might be explained on the ground that in the lower concentrations the acids 

 are so nearly completely ionised as to have about the smite effects, but as the 

 concentration is increased the concentration of hydrogen ions, and consequently 

 the toxicity increases mors rapidly in HNO than in HBr and in HBr than in 

 HgSOj. The data is, however, insufficient to «? arrant any conclusions. In 



H 3 P0 4 (Fig. 24) there was no such marked retardation of regeneration in the 

 concentrations used although the decrease in the total amount regenerated wss 

 squally pronounced. : rate of regensration proceeded at very nearly the 



