6 The Endocrine Organs 



Starling does not, however, confine the use of the term hormone to 

 organic principles of an endocrine nature. His definition is much wider. 

 " By the term ' hormone,' " he says, " I understand any substance normally 

 produced in the cells of some part of the body and carried by the blood 

 stream to distant parts, which it affects for the good of the organism as a 

 whole " (Proc. Roy. Soc. Med., 1914, vol. vii., Therap. and Pharm. Sect., p. 29). 

 He then proceeds to give as examples of hormones, secretine, adrenalin, 

 and carbonic acid — the last, which is produced by the tissues in general 

 and more especially by muscular tissue, stimulating the respiratory centre 

 to activity. Obviously this definition would include many substances 

 normally present in the blood, such as water, urea, glucose, and inorganic 

 salts, which are produced in various parts of the body and affect distant 

 organs such as the kidneys ; indeed it may be supposed that most circulating 

 materials will, when we know more about their history, come into the 

 definition. The expression hormone has not been hitherto employed by 

 physiologists and clinicians in this extended sense ; the term has usually 

 been restricted to the active organic principles of the internal secretions. 

 But it will perhaps be best to employ the term hormone in the sense in 

 which it was used by its inventor, i.e. to denote any substance in the blood 

 which excites cells of the body to activity, and to express by a special term 

 those specific substances which are produced by the organs of internal 

 secretion for the purpose either of exciting or of restraining the activity 

 of other organs. Since the most characteristic feature of the action of 

 these substances is the resemblance to the action of drugs, such as the 

 vegetable alkaloids, I propose to employ for these specific substances the 

 general title autacoid substances, or simply, autacoids (avros, self, and 

 a/coe, a medicinal agent or remedy). I would accordingly define an autacoid 

 as a specific organic substance formed by the cells of one organ and passed 

 from them into the circulating fluid to produce effects upon other organs 

 similar to those produced by drugs. Such effects are either in the direction 

 of excitation, in which case the endocrine substances producing them are 

 excitatory autacoids and would come under the expression hormones, or 

 in the direction of restraint or inhibition, in which case they are restraining 

 or inhibiting autacoids and would be classed as chalones. The action 

 of an autacoid may therefore be described as hormonic or chalonic, ac- 

 cording to the kind of effect it produces. 



Some autacoid substances appear to produce opposite results in different parts. 

 Thus the adrenalin of the suprarenal medulla causes contraction of the plain muscle 



an effect at a distance, whether such effect be excitatory or inhibitory. If, in place of 

 hormone, the expression hermone ('Eppfjs, Mercury) had been selected, the difficulty 

 which is caused by the use of the term hormone, which implies excitation, for agents 

 which act in exactly the contrary manner, would not be felt. Biedl uses the expressions 

 erregende Hormonen and hemmende Hormonen, i.e. excitants which excite and excitants 

 which prevent excitation ! It is true that he regards the one class as exciting katabolic 

 changes and the other as exciting anabolic changes, but this is purely theoretical, and it is, 

 to say the least, improbable that these agents operate in the manner thus indicated. 



