474 MINNA E. JEWELL 



results were obtained in a parallel series of experiments in which 

 the base used was Ca(0H)2. 



The large range of low concentrations was used to see if any 

 acceleration to regeneration might be produced by low concen- 

 trations, such as was found for the development of sea-urchin 

 eggs by Loeb ('98) and Moore, Roaf and Whitley ('05). As the 

 growth curves show, no such acceleration appeared. In fact, 

 the addition of bases produces no appreciable effect until 15 cc. 

 has been added, giving a 0.0075 normal base, in which concen- 

 tration a marked retardation of regeneration appears in both 

 KOH and Ca(0H)2. A comparison of tables 1 and 2 brings out 

 another point. The larger tadpoles (table 1) show a marked 

 retardation of regeneration in 15 and 20 cc. of the base. The 

 smaller tadpoles (table 2), although killed much sooner by these 

 higher concentrations, show no greater retardation of regener- 

 ation in the concentrations next lower — 10 and 15 cc. — than do 

 the larger ones. This subject of the effect of size upon inhibition 

 of regeneration will be more fully discussed later. 



The next series of experiments (fig. 5) was run in order to 

 determine whether the effect of bases upon regeneration is due 

 to the action of the hydroxyl ions or whether the cations or 

 osmotic pressure play an important part. The experiments 

 were carried on in finger bowls each containing four tadpoles. 

 The water was changed alternate days. Although the eighty 

 tadpoles used were of as nearly the same size as could be obtained, 

 they were first divided into four lots, each lot containing tadpoles 

 apparently identical in size. One tadpole from each lot was 

 then put into each of the solutions. This method for obtaining 

 uniformity of size was used in all succeeding experiments where 

 a large number of animals were involved. The first, seventh, 

 and fifteenth dishes were distilled-water controls. In figure 5 

 the '0' line, or curve of growth of the controls, is plotted from the 

 average of these three. This figure shows a progressive and 

 rapid decrease in regeneration in increasing concentration of 

 Na2C03. The tadpoles in 60 and 75 cc. died in four and three 

 days, respectively, without having undergone any regeneration. 

 There is no marked decrease in regeneration in increasing con- 



