PHYSIOLOGICAL FACTORS REGULATING 



NORMAL AND PATHOLOGICAL 



GROWTH 



AN analysis of growth from the causal standpoint is excep- 

 JT\ tionally difficult and in many respects impossible. Living 

 protoplasm of both plants and animals possesses the power to 

 add to its mass more living substance similar in kind. The scien- 

 tific attitude was expressed by Dr. Mendel speaking from this 

 platform when he described certain inherent properties of liv- 

 ing substance as "the growth impulse." This phrase is a recog- 

 nition of the ancestral origin of the chemical or physico-chemi- 

 cal properties of living protoplasm. 



"The growth impulse" in an embryo plant or animal ade- 

 quately supplied with foods and food vitamins is manifested by 

 an orderly but infinitely complicated series of changes in which 

 there is a fairly definite and average cycle of increase in mass, 

 an unfolding of characteristic form, and an intricate differentia- 

 tion of parts all according to laws that have been presented in 

 preceding lectures before this audience. The nature of these 

 changes, the time of the growth cycle, the relations of environ- 

 ment and of foods, and the story of the embryological and tis- 

 sue components — all have been presented. What remains to be 

 discussed is the coincident functional or physiological factors 

 influencing growth. 



We recognize that during the growth in size, and occurring 

 hand in hand with differentiation in structure, there is an or- 

 derly unfolding of function, a differentiation of physiological 

 labor, so to speak. Capacity to function in different ways and to 

 different degrees appears in orderly sequence, and the func- 

 tional acts and processes at once become a part of the environ- 

 ment which henceforth conditions the further development of 

 the individual, both morphologically and physiologically. 



