HORMONES, DRUGS, AND TOXINS 707 



voisins ou situes & distance." Babkin (1914, p. 5)>-ays " Die Hormone bilden die Vermittler 

 zwischen den verschiedenen Teilen des Korpers (Bayliss und Starling)." When, therefore, 

 the name is extended to apply to such substances as chloroform or toluene, which set into 

 activity enzymic changes in cells because they are able to penetrate the cell membrane and 

 enable interaction to take place between constituents within the cell (H. E. and E. F. 

 Armstrong, 1910, 1911), it appears to me that the original meaning of the word is deprived of 

 significance and applied to cases of a different kind, for which there does not seem to exist the 

 necessity for a special name. 



It may be added that this conception of co-ordination by chemical messengers 

 is to be found in a note by Brown-Sequard and d' Arson val (1891), who say 

 " Nous admettons que chaque tissu et plus generalement chaque cellule de 

 1'organisme secrete pour son propre compte des produits ou des ferments speciaux 

 qut sont verses dans le sang et qui viennent influencer par 1'intermediaire de 

 ce liquide toutes les autres cellules rendues ainsi solidaires les unes des autres, 

 par un mecanisme autre que le systeme nerveux." 



When we look around the numerous examples of such influence of minute 

 traces of substances formed by one organ and acting on other organs, we note 

 that there are not many so definite as that of secretin, where the food entering 

 the duodenum causes the production of a special substance which enters the 

 blood and excites the pancreas to pour into the duodenum a digestive juice, 

 and, so far as we know, does not act on any other organ except the liver, whose 

 secretion is an adjuvant to that of the pancreas. 



Gley (1911, p. 19) rightly calls attention to the fact that some of the 

 substances which act like hormones in modifying the activity of distant organs, 

 such as carbon dioxide on the respiratory centre, are really products of the 

 ordinary metabolism of cells, and are not, like secretin, produced for a specific 

 purpose. The delicate sensibility of a particular nerve centre to carbon dioxide 

 must be supposed to be an adaptation developed in the course of evolution. 

 Gley suggests calling these latter substances " parahormones." He also points 

 out the convenience of a name for that class of hormones which influence growth, 

 and proposes that of harmosones (from ap/j.6<, I regulate or direct). 



When distinction is required between the different classes of hormones, these names 

 appear satisfactory. On the other hand, the distinction made by Schafer (1913) between 

 substances which excite (hormones) and those which depress (chalones) activity, seems 

 unnecessary, as also the name "autacoid" to include both. If we interpret, as we are 

 justified in doing, "excitation to activity" as being equivalent to "bringing into play an 

 influence on cell processes," this influence may be of such a nature as to inhibit. Moreover, 

 such a typical hormone as adrenaline excites blood vessels to contraction, but inhibits the 

 muscular coat of the intestine, so that it is both hormone and chalone, according to the 

 particular way in which the sympathetic end organ, on which it acts, terminates in the cell. 



The name " internal secretions " has been given to many of the substances 

 with which we are here concerned ; this was done before the discovery of secretin. 

 The fact that many organs deliver the products of their activity into the 

 blood current was well known to Claude Bernard (1859, ii. pp. 411, 412), and 

 the name "internal secretion" is due to him. The products of organs such as 

 the suprarenals, the thyroid, and so on, are those to which the name is given. 



Before we pass on to consider some facts in relation to various individual 

 hormones, the considerations of Hopkins, to which attention was directed above 

 (page 20), should be remembered. An intermediate product in a chain of 

 reactions, although its concentration in the system at any given moment may be 

 infinitesimal, is probably of great importance as a necessary stage. The amount 

 present may be small because the rate of the reaction producing it may be slow, 

 compared with that of the reaction by which it is changed into a further product. 



INDIVIDUAL HORMONES 



Secretin. As already pointed out, the most typical of all the chemical messengers 

 is that which causes secretion of pancreatic juice when acid enters the duodenum. 

 This mechanism was described in a previous chapter (pages 344 and 346). 



The view of Popielski that the effect on the pancreas is merely due to the 

 presence of a vaso-dilator substance is easily disproved in many ways. Bayliss 



