REMOVAL OF PRONEPHROS OF AMBLYSTOMA 359 
this process is sure to be almost entirely one of hypertrophy, not 
a hyperplasia, of the kidney elements. In the glomerulus and 
urinarj^ tubules the former process occurs exclusively, in the 
epithelial cells themselves, hypertrophy with a negligible amount 
of hj^perplasia. 
The clearest and by far the most accurate statement of the 
exact histological conditions found in the hypertrophied kidney 
is given, however, by Galeotti and Villa Santa ('02). These 
authors approached the problem from a widely different view- 
point, their main object being to determine whether the hyper- 
trophied kidney of an adult animal would show the same histo- 
genetic potency as that of an animal which had not attained its 
full growth. From their study of the kidneys of young and 
adult dogs and rabbits, careful estimates were made of the num- 
ber of glomeruli found in sections of normal and hypertrophied 
kidneys and of the relationship between the average surface 
area of the glomeruli and the number present. Furthermore, 
the diameter of the lumen in the tubuli recti was accurately 
measured and the secreting surfaces in the two kidneys obtained 
for comparison. The volumes of the cell walls in the two cases 
were also computed and contrasted. The thoroughness of the 
methods used in these computations gives added weight to their 
conclusion that, whereas in the young kidney hyperplasia may 
occur, the adult kidney has lost its potency for addition of new 
parts, and can only respond by the enlargement of those elements 
already present. 
Kittleson ('20), in his recent report on the effects of inanition 
and refeeding on the growth of the kidneys in young rats, con- 
firms the opinion of former workers that starvation inhibits the 
formation of renal corpuscles, and further concludes that "refeed- 
ing after stunting results not only in a hypertrophy of the renal 
corpuscles but also in an increase in number, which may even 
exceed the normal." This would indicate the possibility of both 
hypertrophy and hyperplasia of the same kidney element, 
induced by these abnormal conditions. 
No instances are on record of experiments dealing with the 
production of hypertrophy or hyperplasia in the adult am- 
