470 MINNA E. JEWELL 



produced by the tadpole during the given time. This method 

 of CO2 determination is based upon the assumption that all of 

 the acid produced by the organism is CO2, or that other acids, 

 if produced, are in negligible quantities. 



The hydrogen ion concentration was determined by the method 

 of McClendon ('16). The solution to be tested was placed in a 

 test-tube 1-cm. bore, and 0.1 cc. of the indicator solution added. 

 It was then compared with the color chart by looking down into 

 the tube against a white background. The indicators used were 

 butter yellow (dimethyl amido azobenzene), methyl orange, 4 

 Br-phenol-S-phthalein (brom phenol blue), methyl red, parani- 

 trophenol, neutral red, 2 Br-thymol-S-phthalein (thymol blue), 

 phenolphthalein and thymolphthalein. Solutions of methyl 

 violet and tropaeolin 00 (orange IV) were also prepared, but 

 none of the solutions used were so acid as to come in their range. 

 On the other hand, the basic solutions went beyond the range 

 of the color chart, so the hydrogen ion concentrations of only 

 the more dilute solutions could be determined. 



This method, as applied, is at best only approximate, for, in 

 the first place, the comparison of a transparent solution with an 

 opaque paper color chart is difficult, and gives great scope for 

 personal equation, and, in the second place, where the solution 

 employed caused extensive injury to the animal it is probable 

 that amino acids and other organic compounds from the degen- 

 eration tissues were set free in the solution. Such substances 

 may affect the delicacy of the indicator. 



PRESENTATION OF DATA 



Before beginning the experiments on regeneration, a test was 

 made to determine approximately the concentration to use. 

 0.01 and O.OOIN solutions of each of the bases and acids to be 

 tested (except NaaCOs and H3PO4 0.01 and 0.001 mol.) were 

 prepared, and a tadpole put into 1 liter of each. The length of 

 life was noted as follows: 



