46 PIGMENTARY GROWTH AFTER ABLATION OF 



32-mm. stage (midlarval period) is reached. At this stage the 

 retardation becomes extremely pronounced and an abrupt change 

 in the direction of the growth curve ensues. So definite and 

 so characteristic is this point that it appears to indicate a sig- 

 nificant period in the development of these albinous larvae and 

 hereafter will be designated as the 'critical point.' Both in 

 time and stage of development this point has been coincident 

 in the curves plotted from data secured in 1918 and 1919. From 

 this 'critical point' the divergence between the curves of the 

 normal and albinous larvae increases for a time, the curves 

 later approaching each other again due to the onset of meta- 

 morphosis in the former and the continued growth of the latter. 28 



It is now possible to inquire whether the administration of 

 a 'substitution' or 'replacement' diet of fresh bovine anterior 

 lobe will effect a normal rate of growth in these animals suffering 

 from hypophysial deprivation. This can be answered for the 

 frog tadpole in the affirmative. The albinous frog tadpoles sup- 

 plied throughout their growing period with a continuous diet of 

 fresh anterior-lobe substance exhibit no significant growth devia- 

 tion from the liver-fed normals (fig. 1, table 2). Since meta- 

 morphosis does not supervene, however, their growth extends 

 beyond the normal larval period, and they consequently attain 

 a size notably in excess of their unoperated normal fellows. 29 

 The alimentary regime of fresh bovine anterior lobe has then 

 clearly supplied the morphogenic principle lost by buccal hypo- 

 physectomy. 



It is conceivable that pituitary substance greatly in excess 

 of the amount actually requisite to replace the growth principle 



28 It will be noted from the tables that after September 7th a continuous diet of 

 fresh bovine anterior lobe was supplied the albinos whose curve of growth is here 

 plotted. This apparently caused an abrupt rise in their growth curve. The growth 

 curves of a group of albinos supplied throughout their life-span with a liver diet are 

 shown on page 18 (Smith, '18). 



29 The final and rather abrupt termination in growth exhibited by the* albinous 

 specimens might conceivably be due to one of at least two factors: 1) a self-limiting 

 growth factor inherent in every organism; or, 2) a seasonal growth rhythm. That 

 this is not attributable to the latter is shown by a group of albinous frog larvae 

 which survived for seventeen months. No resumption of growth occurred in the 

 second season; rather, they became progressively more lethargic, the anorexia in- 

 creased, and death finally supervened. 



