REGULATORY PROCESSES IN ORGANISMS 205 
on whether the one or the other of these processes is the more 
rapid. Hypertrophy is then in no sense a ‘regeneration in excess’ ; 
it is merely a direct result of increased metabolic reactions of the 
kind which constitute or accompany the ‘function’ of the part 
concerned. Nevertheless, it is without doubt a compensation. 
The occurrence of one series of metabolic reactions determines the 
occurrence of another series according to chemical laws; the one 
series furnishes energy, the other forms relatively inactive sub- 
stances, which persist as structure. Closely related to functional 
hypertrophy is the growth in size of regenerating parts after their 
formation: here the ‘fuactional stimulus’ is the quantitative 
factor in the correlative influences from other parts. This factor 
induces a certain rate or frequency of reaction in the small new 
part, which leads to rapid accumulation of material, 7. e., to hyper- 
trophy (Child, ’06a, p. 407). But as the structural substance 
accumulates, the structure itself constitutes an obstacle to metab- 
olism (Child, *116) the rate of hypertrophy decreases and finally 
equilibrium is attained. 
c. Regulatory transformation. The character of many metabolic 
reactions 1s more or less definitely known, but the exact relation 
of the reactions to the production of a particular kind of visible 
structure is a much more difficult matter to determine. The 
visible characteristics of organic structure are by no means ade- 
quate criteria of the character of the processes involved in its 
formation. We are not always justified in concluding from the 
differences in the visible appearance of structures that the proc- 
esses concerned in their formation are actually different in nature. 
Great differences in appearance may arise in the same colloid 
substance in consequence of differences in aggregate condition 
or phase. But when we find substances of different constitution 
in different cells or parts, it is evident that processes of different 
character were coacerned in their formation. Consequently we 
can often determine that a transformation has occurred by the 
change in the character of the structural substance. Many fea- 
tures of correlative differentiation, whether in ontogeny in nature 
or under experimental conditions are undoubtedly transforma- 
tions, e. g., the formation of a bud from a differentiated cell in 
