RELATIONSHIP OF ENDOCRINE ORGANS TO GROWTH 493 



capacity to grow, as the above-cited investigations of Osborne and 

 Mendel reveal, is not determined by age but, as we have already con- 

 cluded upon other grounds, by a lack of balance between the forward 

 and opposed reactions of tissue-synthesis and tissue-degradation, so 

 that upon admission of the necessary substrates, no matter what the 

 age prior to the death or senescence of the animal may be, growth 

 occurs and continues until equilibrium, or equality of the velocities of 

 tissue-synthesis and tissue-degradation is attained. We thus reach 

 once more, and from a totally different angle, the conclusion that 

 the relatively stationary weight of an adult animal is determined 

 by the accumulation of the Products of Growth, and not in any sense 

 by the exhaustion of its Substrates. 



THE RELATIONSHIP OF THE ENDOCRINE ORGANS TO 



GROWTH. 



We have seen that the chemical processes which underlie the growth 

 of animals are of such a nature that they produce their own catalyzers. 

 But if this be so then we are immediately impelled to the conclusion 

 that Catalyzers of Growth exist, i. e., substances which, perhaps in 

 minute proportion, and certainly quite independently of their nutritive 

 or substrate- value may profoundly modify the growth of living tissues. 

 The question now arises whether any evidence other than evidence of 

 this inferential kind is obtainable of the veritable existence of such 

 endogenous catalyzers of growth? 



In the simpler undifferentiated organisms the catalysis of growth, in 

 common with all the other vital processes, is doubtless a function of 

 every cell, and each cell contains the necessary materials for the accel- 

 eration of the production of living matter. In the higher and more 

 differentiated organisms, on the other hand, it is not at all improbable 

 that the function of growth-catalysis is, to a greater or less extent, 

 delegated to special cell-groups or organs, just as the function of motility 

 is delegated to muscle-cells, that of conductivity is especially displayed 

 by nerve-fibers, and those involved in digestion are delegated to the 

 alimentary canal and dependent organs. We are thus led to direct 

 our attention to the possibility of the existence in the body of special 

 cell-groups exercising to an exceptional degree the function of growth- 

 catalysis. 



The profound significance of certain of the various Endocrine Organs 

 or glands of internal secretion in the processes of growth immediately 

 suggests that these are the special cell-groups to which the function of 

 growth-catalysis is most particularly delegated. We know from 

 abundant clinical experience that disorders of the thyroid, thymus, 

 sexual glands and particularly of the anterior lobe of the pituitary 

 body, are reflected in a profoundly disturbed development of the 

 various tissues of the body, while the action of the secretions of the 

 Corpora Lutea in stimulating the outgrowth of placentae from the wall 



