HORMONAL CONTROL 



549 



growth and phototropic bending are mediated by such substances, the most 

 fully knowai among which are auxins. In the simplest unicellular animals the 

 same mechanism of the diffusion of the chemical products of metabolism 

 plays an essential role in the activities of the organism, and although in the 

 higher animals greater reliance is increasingly placed on the more efficient 

 and adaptable nervous mechanism, chemical coordinators are still retained, 

 particularly to mediate those functions for which the controlling influence 

 is required to last over considerable periods of time — growth and cellular 

 differentiation, general metabolism, sexual activity, and so on. The spheres 

 of influence of nervous and chemical control are by no means mutually 

 exclusive for while a sudden response may be 

 induced by the nervous mechanism, it is frequently 

 maintained by the chemical, as is exemplified in the 

 reaction of the sympathetic and the adrenals to 

 situations of stress, or the comj)lementary activities 

 of nervous and chemical agencies in effectmg changes 

 in the chromatophores of Insects and teleostean 

 Fishes. Chemical stimulators (or inhibitors) speci- 

 fically elaborated to jjroduce such effects are termed 



HORMONES. 



Fig. 720. — Vesalius's 

 Conception of the 

 Funnel (Infundibu- 

 lum) (B) through 

 WHICH THE Phlegm 

 FROM THE Brain 

 Trickled into the 

 Pituitary Gland (A). 



The four iinaginary 

 ducts C, D, E, F, carried 

 the phlegm from the 

 gland (Zuckernian). 



The conception of hormones recalls the old theory of 

 the humours which derived from the Aristotelian conception 

 that all things were inade up of the four common elements 

 — earth, water, air and fire. The fovir humours which 

 pervaded the body and determined its health — yellow bile 

 (choler) from the gall-bladder, black bile (melancholy) from 

 the spleen, blood (sanguine) froiu the liver, and pituita (or 

 phlegm) from the brain. The conception of Vesalius that the 

 phlegm secreted from the brain escaped by way of the 



infundibulum into the pituitary gland and thence was distribvited throughout the 

 body is very akin to the most modern conceptions of neuro -endocrine secretion that 

 we are now to consider (Fig. 720). 



The fact that organs deliver the products of their activity into the blood-current 

 and thus influence bodily functions was known to Claude Bernard (1859) who introduced 

 the term " internal seci'etions." The word hormone {op^doj, to rouse to activity), 

 suggested by W. B. Hardy, was first apjilied to animal physiology by Starling (1905) 

 with reference to the discovery of the manufacture of secretin by the pancreas (1902). 

 The word was first applied to plant physiology by Fitting (1910) who found that a 

 substance in the pollen of the orchid caused a swelling of the gynosteinium of the 

 flower. In botany the teriu phytohormones is often used, or, as the Russians have it, 

 florigens (Cailahian, 1940). Since, in association with Sir William Maddox Bayliss, 

 SIR ERNEST HENRY STARLING (1866-1927) was the discoverer of the first specific 

 hormone and in view of his immense contributions to physiology in other fields, such 

 as the nature of the body-fluids, the control of the intra-ocular pressure and a host 

 of other equally revolutionary conceptions, I am introducing this section with his 

 photograph (Fig. 719). My personal indebtedness to him as Professor of Physiology 

 in University College. London, where he initiated me into the techniques of research, 

 is indeed great. 



