498 MINNA E. JEWELL 



which most of them died. In such a concentration the few which 

 survived underwent very Httle regeneration. In a concentration 

 in which most of the tadpoles hved, however, if the per cent 

 regenerated by each tadpole be divided by the per cent regener- 

 ated by its respective control, the result is approximately the 

 same for all sizes. This would indicate that the effect of an acid 

 upon regeneration is relatively independent of the size of the 

 tadpole; that the effect is probably largely local upon the regener- 

 ating tissue until a concentration is reached which seriously 

 affects the tadpole as a whole, after which regeneration is retarded 

 by the acid both directly and indirectly because of the impaired 

 health of the parent animal, upon which the new growing tissue 

 is dependent for nutriment. This point is reached in the smaller 

 individuals before it is in the larger ones. 



These experiments, while few in number, would suggest the 

 use of abnormal conditions, such as those produced by chemicals, 

 as a promising method of attack for investigations upon the 

 relation between new tissues and the organism as a whole. 



Regeneration m low oxygen 



The method of obtaining a gradient of oxygen has already 

 been described (p. 4(56). For the first series of experiments three 

 tadpoles of different sizes were placed in each of the seven experi- 

 mental jars. During this experiment the water was strongly 

 basic to phenolphthalein, though acid to thymolphthalein. Of 

 the larger tadpoles, 70 to 77 mm., the one in the first jar (oxygen- 

 free water) died without regeneration, and no. 3^ — in 1.6 cc. O2 

 per liter^ — showed better regeneration than nos. 5 and 6 — in 

 3.03 and 3.8 cc. O2 per liter, respectively. This is doubtless 

 accounted for by the fact that nos. 2 and 3 remained most of 

 the time at the surface of the water, while nos. 4, 5, 6, and 7 

 remained at the bottom, coming to the top only occasionally. 

 When the fact that the water in which nos. 2 and 3 actually re- 

 mained contained considerably more oxygen than was shown by 

 the titrations is taken into consideration, these data show clearly 

 a relation between regeneration and the oxygen content of the 

 water. The same thing is true of the medium-sized tadpoles. 



