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SCIENCE 



[N. S. Vol. XXXI. No. 786 



placed for the most part by a kind of sym- 

 biosis, such that the products of metabolism 

 in one tissue serve as a stimulus to the 

 activities of other tissues. If a muscle is 

 stimulated to greater growth by an excess 

 of functional activity the substances given 

 off to the blood during its metabolism act 

 favorably upon the growth of other muscles 

 which are not directly concerned in the in- 

 creased work, or upon the connective tissue 

 surrounding and permeating the muscular 

 mass; and conversely, the development of 

 connective tissue from any cause aids di- 

 rectly by its secretions or excretions in the 

 growth of the muscle. There is thus es- 

 tablished a circulus henignus by means of 

 which each tissue profits from the func- 

 tional activity of its fellow tissues. From 

 many sides and in many ways facts have 

 been accumulating which tend to impress 

 the general truth that the co-activity of the 

 organs and tissues may be controlled 

 through chemical changes in the liquid 

 media of the body, as well as through nerve 

 impulses, but in physiology at least we owe 

 the definite formulation of this point of 

 view to Bayliss and Starling. Through 

 their investigations upon secretin they ob- 

 tained an explicit example of how one 

 organ controls the activity of another organ 

 by means of a specific chemical substance 

 given off to the blood. Other facts known 

 in physiology in regard to the internal 

 secretions were easily brought into line 

 with this definite instance furnished by the 

 secretin, and Starling's convenient term of 

 "hormone," as a general designation for 

 such substances, has served to give a wide 

 currency to the conception. The word and 

 the generalization implied by it have been 

 adopted by investigators in many fields of 

 biological research to explain phenomena 

 of correlation which heretofore it has been 

 impossible to bring under the general 

 rubric of nervous reflexes; phenomena 



which in fact it has been difficult to express 

 clearly in any precise way such as might 

 serve to stimulate direct experimental in- 

 vestigation. An interesting example of 

 this application of the term and the idea 

 contained in it is found in the theory ad- 

 vanced by Cunningham to explain the 

 development and inheritance of secondary 

 sexual characteristics. This author con- 

 structs a system of hypothetical hormones 

 which, if present, would account not only 

 for the development of the secondary 

 sexual characters, as the result of the ac- 

 tion of specific hormones furnished by the 

 reproductive cells, but would also make 

 conceivable a method by which these secon- 

 dary characters, like other somatogenic 

 characters, might affect the germ cells in 

 turn in such a definite way as to be trans- 

 mitted to the following generations. It is 

 not my purpose to criticize this or similar 

 theories. They will doubtless serve a good 

 purpose in stimulating and directing in- 

 vestigations. It does, however, seem prob- 

 able that the term hormone, like some of 

 the useful terminology of immunology, 

 will be overworked, and that investigators 

 may deceive themselves as well as others 

 when they conclude that any given rela- 

 tionship is an example of hormone regula- 

 tion. It has occurred to me that it may be 

 useful in connection with this symposium 

 upon the internal secretions to review very 

 briefly the state of our knowledge in re- 

 gard to the hormones, with the purpose of 

 discussing somewhat the probable nature 

 of their action and the extent of their dis- 

 tribution. 



In treating this subject one must con- 

 sider also the more or less nearly related 

 instances of combined activity of a chem- 

 ical sort which are expressed by such terms 

 as chemical activators, kinases and co-fer- 

 ments. These terms like that of hormone 

 are relatively new, they have been brought 



