Nature of the Active Principles of the Internal Secretions 5 



and they are readily destroyed by heat in presence of water. The active 

 materials of the endocrine organs, on the other hand, are for the most part 

 not rendered inactive even by prolonged boiling, and are certainly of a 

 much simpler chemical constitution than enzymes. They are dialysable ; 

 and although most of them have not yet been isolated in a crystalline form, 

 due probably to the fact that it is difficult to obtain them free from im- 

 purities, some of them have been so obtained, and at least one — the active 

 material of the adrenal medulla — has been prepared synthetically. Many 

 of them act instantly ; their action, as Starling has pointed out, being similar 

 to that produced by the active principles of drugs, especially those of organic, 

 i.e. of vegetable, origin. These also operate by immediate chemical action, 

 being conveyed to the parts which they influence in solution in the circu- 

 lating blood. But while some of the materials of the internal secretions 

 produce their effects upon the tissues immediately, others operate more 

 slowly, so that the results of their action may only become apparent after 

 a prolonged period of time. The latter class usually exert their influence 

 upon the growth and nutrition of special organs or of the body generally ; 

 they are accordingly termed by Gley morphogenetic. 1 None of the sub- 

 stances we are dealing with are known to cause the production of anti- 

 bodies when introduced into " foreign " blood. Their action is similar in 

 all animals, however different from the animal yielding the secretion. 



As with drugs, some of the principles yielded by the endocrine organs 

 act by stimulating or exciting cell-functions : this is notably the case with 

 the principle obtained by the action of acid on the duodenal epithelium. 

 Others depress or inhibit those functions : an example of this is met with 

 in extract of placenta, which when injected into the blood-vessels tends to 

 prevent the secretion of milk. To such stimulating principles as that con- 

 tained in the extract of duodenum after treatment with acids the term 

 hormone (from opfidoo, to stir up) was originally applied by Starling, 2 and 

 the expression has been extended to include the active principles of all 

 internal secretions. So long as only exciting agents were known, there 

 could be no objection to this extension of the term, but since agents which 

 produce depression or cessation of function have been shown also to be 

 produced in the body — and their number will probably become considerable 

 as the nature of the internal secretions is more fully examined — it is advis- 

 able to employ an expression which will discriminate between these and 

 the stimulating agents. On this account I propose to distinguish the action 

 of the depressants from that of the excitants by the use of the term chalone 

 (xaXao), to make slack). A chalone may therefore be defined as an 

 endocrine product which inhibits or diminishes activity, as distinguished 

 from a hormone, which excites to increased activity. 8 



1 He suggests the name harmozones for them (apn6(u, to govern). 



* VerhandV. d. Naturforscher-Versammluny, Stuttgart, 1906. 



3 The original expression employed by Bayliss and Starling (Journ. Physiol^ xxviii., 

 1903) in their paper on secretine was chemical messenger. This is more appropriate 

 as a general term than hormone, because it includes all chemical agents which produce 



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