CHAPTER XXIV 

 HORMONES, DRUGS, AND TOXINS 



THAT there are a number of poisonous substances which act on living organism- 

 in very minute doses has been known for centuries, but the fact that there are 

 also many chemical compounds which are indispensable to the normal activities 

 of organisms, although present in infinitesimal amount, has been recognised, 

 in its full import, only in recent years. We have seen instances in the " accessory 

 factors" of diet (pages 254-261), in the chemical mechanism of secretion, and of 

 vascular dilatation and constriction, as wett as in enzymes and catalysts in general. 

 In most of these cases the active substance is present in such extraordinarily 

 small amount that, at present, it seems almost impossible to discover its nature. 

 In some few cases the chemical nature is known. 



The Minuteness of the Quantity necessary is made clear by the work of Bertrand on 

 the action of zinc and manganese (pages 221-222 above), and that the phenomenon 

 is not peculiar to living protoplasm is shown by the experiments of Elissafov on 

 the action of thorium on the sign of the electric charge on surfaces. Thus the 

 presence of 0*2 mg. of thorium nitrate in a litre of water lowered the rate 

 of movement through a quartz capillary, under the action of electric forces, by 

 50 per cent. Other cases will appear presently. The nature itself of catalytic 

 action, indeed, implies that only a very minute amount of a catalyst is necessary in 

 order that an effect may be produced. 



HORMONES 



When we came across the mode by which the pancreas is excited to activity, 

 it became obvious, to Starling and myself, that the chemical agent concerned 

 is a member of a class of substances of which others were previously known. 

 The peculiarity of these substances is that they are produced in one organ, and 

 carried by the blood current to another organ, on which their effect is manifested. 



Since some confusion has been introduced into the nomenclature of the subject, a few 

 words are necessary as to the history of the name. 



The group of substances referred to, which includes adrenaline and the various internal 

 secretions, is characterised by the property of serving as chemical messengers, by which the 

 activity of certain organs is co-ordinated with that of others. They enable a chemical 

 correlation of the functions of the organism to be brought about through the blood, side by 

 side with that which is the function of the nervous system (see the Croonian Lecture by 

 Bayliss and Starling, 1904). This being so, it seemed desirable and convenient to possess 

 a name to distinguish the group. That of " internal secretions," already in use, did not 

 sufficiently emphasise their nature as messengers. After the discovery of secretin, this name 

 for the group was for long time a subject of discussion in the laboratory, but no satisfactory 

 name was suggested. Finally, Mr W. B. Hardy proposed the name "hormone," derived 

 from opfidu ("I arouse to activity"), and, although the property of messenger was not 

 suggested by it, it was adopted. It has, in fact, been generally understood as having the 

 meaning intended, and not to be applied to any kind of substance which excites activity. 

 Indeed, a name of such very wide application would be of comparatively little value. I may 

 give three quotations to show that this property of messenger is usually understood in the 

 use of the word "hormone." Gley (1911, p. 19, footnote) points out that the "excitants 

 fonctionnels (hormones de Bayliss et Starling) " are of two kinds. We shall presently return to 

 this distinction, but the point is that Gley insists on the correlation established between 

 different organs " par 1'intermediaire de substances secretees par des glandes speciales et 

 deversees dans le sang qui les transport* la ou elles peuvent agir" (p. 21). Again, Hustin 

 (1912, p. 319) says " Bayliss et Starling donnerent le nom cThormonffi (6pfuiu, j'excite) ces 

 substances qui constituaint, comme la 9ecrttine, des intermediates chimiques entre des organes 



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