ENVIRONMENT AND REGENERATION 



471 



Two controls were run; one distilled water from the metal 

 still (this water was used in making up the solutions) and the 

 other, to eliminate the possibility of osmotic pressure having 

 produced the effect, a solution consisting of 37 parts 0.01 mol. 

 KH0PO4 and 63 parts 0.01 mol. NasHPO., which is the neutrality 

 buffer solution of Levy, Rowntree and Mariott ('15) diluted to 

 0.01 mol. In the former the tadpoles lived five days, in the latter 

 thirty-eight days. 



It will be noted with regard to the bases that in both concen- 

 trations the tadpoles in NH4OH, the weakest base, died first. 

 For this reason, as the specific toxicities of the various substances 

 were not within the scope of this investigation, NH4OH was not 

 used in subsequent experiments. The difference in length of 

 life of tadpoles in 0.001 N. KOH and NaOH (thirty-one and five 

 days) is not so significant as it at first appears. Both solutions 

 produced very serious effects upon the tadpoles during the first 

 few days. The skin became white, the margins of the tail 

 degenerated, and both specimens appeared on the point of death. 

 A test of the water made the fourth day showed that it was then 

 practically neutral. From this time on the tadpole in KOH 

 gradually recovered, but its companion in NaOH succumbed. 

 It would seem, however, and subsequent experiments tend to 

 show, that the considerable difference in length of life was caused 

 by a slight difference in the resistance of the two individuals. 

 Similarly the death of the tadpole in NagCOs after six days was 

 not regarded as showing any specific toxicity of that substance, 

 although the death of the tadpole in Ba(0H)2 after thirty-six 



