38. 

 abnormally low regeneration of the tadpoles of that also la the first oontrolV 

 A comparison of this experiment with Fx?*riment 18 (Table 27) sesms to suggest 

 that the depression of regenerat ion duo to acids la practic-lly the same for 

 sll alias of tadpoine until a concentration is reached which is soon fatal to 

 ths smaller onas. Tn such a concentration, those email ones which survive 

 to re<renar:»te, shoa • strong iepression of regeneration (Table 27). This would 

 indicate that the threshold of toxioity of ths lower animals is lower in relation 

 to the threshold of depression of metabolism than in the larger animals or, in 

 other *ords, that the effaet of the environment upon the regenerating tissue is 

 eomp-ratively independent ot its effect upon the tadpole as a whole. While 

 the data hers presented are both too meager and too inconclusive to warrant 

 an7 conclusions, these experiments and observations upon animals of various 

 sixes in ths previous experiments hr?ve led the author to regard this aa a 

 promising method o! a'-taok for future investigations upon the relation between 

 aew tissue and the organise as a whole. 



Rsgeneration i& Low Oxygen . 



The met nod of obtaining a gradient of oxygen has already been 

 described. For the first S3ries of experiments three tadpoles of different 

 sisee were placed in each of the seven experimental jars. Durinr this experimsnt 

 the water was strongly basic to Phonolpth-*lain though acid to Thytaolpthalein as 

 no attempt was made to acidulate the water. The data for the larger tadpoles, 

 70 to 77 ram. , are given in Table £9. The tadpole in the first Jar (oxygen free 

 uater) died without regeneration. Tha curve of growth (Fig. 34) of No. 3-in 

 1.6 o.o. O3 per liter - lies above those of 5 and 6 - in 3.03 and 3.8 •••« 2 

 per liter respectively. This is doubtless accounted for by the faot th«t 

 •I oa. 2 and 3 remain*! most of the time at the surface of the water, while 

 Nos. 4, 5, 6 and 7 regained at the bottom, earning to the top only occasionally. 



