42 PIGMENTARY GROWTH AFTER ABLATION OP 



not only catch up to the normals, but actually, at about one 

 year of age, come to surpass the normals in weight." Later 

 he says (Robertson, '19): "The computation of the deviations 

 in terms of probable error units shows that the effect of the 

 dosage of pituitary tissue administered upon the growth of 

 the male animals was of uncertain significance, since the observed 

 deviations were only from one to two times the probable error. 

 That the deviations from the normal nevertheless were real 

 and due to the administration of the pituitary tissue is evidenced 

 by the much greater effect of the same character upon the female, 

 consisting of a retardation during the earlier stages of growth. 

 In both males and females the deviations from the normal after 

 the 30th week are of indeterminate significance; that is, the 

 growth curves of the normal and of the pituitary-fed animals are, 

 so far as our estimates reveal, identical after seven months of 

 age. Hence the preliminary retardation of growth has clearly, 

 prior to the 30th week, been succeeded by acceleration." That 

 a transient growth retardation in the young animal results from 

 pituitary administration seems evident not only from the work 

 of Robertson ('16, '19), but from that of Cerletti ('07), Sandri 

 ('09), Aldrich ('12), Wulzen ('14). But that any subsequent 

 acceleration which may be exhibited is due to anterior lobe 

 administration is not clear. Indeed, it seems not improbable 

 that such an acceleration is compensatory, such as Osborne 

 and Mendel have shown to occur with an adequate diet after 

 an animal has been stunted by undernutrition. This seems the 

 more probable in view of Robertson's feeding experiments with 

 Tethelin in which he was forced to abandon the view which 

 he had previously strongly urged — that his alcoholic anterior 

 lobe extract (Tethelin) supplied a growth-accelerating principle. 

 These animals, indeed, exhibited a more pronounced secondary 

 acceleration when the Tethelin diet was withdrawn than when 

 it was continued. 



The principle has been formulated by Halsted that a 'physio- 

 logical deficit' is essential for successful organ transplantation. 

 From analogy it seems not improbable that if a physiological 

 deficit could be created in experimental animals, they would 



