264 



Supplement to ''Nature^' August 18, 1923 



the greater part of his Croonlan lectures to demonstrate 

 the part played by chemical substances or hormones in 

 co-ordinatinj; the functions of the body he clearly realised 

 that hormone control formed the basal machinery of 

 all evolutionary processes in the animal kingdom. 



"In the lowest organisms, such as the bacteria 

 and protozoa, the only adaptations into which we can 

 gain any clear insight are those to the environment 

 of the organism, and in these cases the mechanism 

 is almost entirely a chemical one. ... In the 

 lowest metazoa, such as the sponges, there is still no 

 trace of any nervous system. The co-ordination 

 between the different cells of the colony is still 

 determined by purely chemical means. ... If, as 

 I am inclined to believe, all the organs of the body 

 are regulated in their growth and activity by chemical 

 mechanisms, similar to those I have described, an 

 extended knowledge of hormones gives complete 

 control of the body." 



We are justified, on all grounds, in looking upon 

 the human embryo, in the earlier stages of its develop- 

 ing, as a colony of protoplasmic units or cells, organised 

 under a system of government controlled by hormones. 

 Each member of the colony, we must suppose, has the 

 power of circularising, by means of the hormone 

 postal system, some or all of the other members of the 

 colony in such a way as to notify its needs and compel 

 their co-operation. With each step in the differentiation 

 of the embryonic tissues there must be a further 

 elaboration in the hormone system of intercommunica- 

 tion and government, until the foetal stages are reached, 

 when the growth-regulating substances become installed 

 in special controlling centres represented by the glands 

 of internal secretion — the pituitary, adrenal, thyroid, 

 etc. We know that juices expressed from embryonic 

 tissue contain substances which stimulate the prolifera- 

 tion and growth of living tissues ; we know from 

 observations already cited that one group of embryonic 

 cells can control the manner in which another group 

 develops, but we have to admit, also, that our know- 

 ledge of the action of hormones in fashioning the growth 

 of organs is still in its infancy. The vista presented by 

 this unexplored field of knowledge is infinite in extent 

 and complexity, and will provide embryologists with 

 many centuries of labour. Their lal)our will reveal in 

 full the true nature of the machinery which underlies 

 the production of structural adaptations which occur 

 in every part of the animal body in every stage of its 

 evolution. 



The Significance of Acromegaly. 



A long and close study of the bodies of men and 

 women who have been the subjects of that strange 

 disorder of growth known as acromegaly, has convinced 

 me that the system of hormones, which controls and 

 co-ordinates the growth of various organs and parts 

 of the body is organised, like the nervous system, on 

 a reflex basis. There are reflexes of growth just as 

 there are reflex actions of muscles ; both kinds of 

 reflexes serve definite purposes in the economy of the 

 body. The glands of internal secretion provide sub- 

 stances which control the action of organs and of 

 parts of the body ; they also produce substances 

 which co-ordinate the growth of the organs or parts 

 concerned in these actions. In the subjects of acro- 

 megaly the pituitary gland is enlarged and its structure 



more or less disorganised ; the parts of the lx)dy which 

 respond to hard toil, such as the hands, feet, and jaws, 

 become greatly and irregularly overgrown. All the 

 systems of the lx)dy — muscular, bony, respiratory, 

 circulatory, alimentary, and renal systems — are in- 

 volved ; all show an abnormal degree and kind of over- 

 growth. 



We find a clue to most of the growth disorders ol 

 the human body, such as acromegaly, in a knowledge 

 of the mechanism of normal growth. Growth dis- 

 orders — dwarfism and giantism — are but derangements 

 of the various parts of the normal machinery of growth. 

 Sir James Mackenzie regards the symptoms of illness, 

 manifested by suffering men and women, as de- 

 rangements of the normal reflex functions of their 

 bodies. In a like manner we may consider disorders 

 of growth, such as acromegaly, as a derangement of 

 a normal mechanism — that which co-ordinates the 

 response made l)y the \arious parts of the Ixjdy to 

 exercise and training. When a man passes into train- 

 ing, whether it be to use his hands as a labourer, his 

 biceps as a blacksmith, his legs as a runner, or his 

 arms as a rower — the responsive growth is not confined 

 to the muscles of his hand, arm, or leg. All the liones 

 of the body respond to a greater or less degree, so do 

 the heart and lungs, so do all the systems of his Ixxly ; 

 he has to eat and digest more. We cannot imagine 

 such a co-ordinated functional result being brought 

 about, one which affects every system of the lx)dy, 

 unless we postulate a controlling system of hormones. 

 Nor can there be a doubt that acromegaly, in all its 

 stages and degrees, represents a diseased manifestation 

 of this adaptational system. 



To fit all the bits of this puzzle into a connected 

 whole we have to suppose that muscles in sustained 

 action do emit certain substances which pass into the 

 circulation and thus reach the pituitary gland. We 

 have to suppose that in the pituitary these substances 

 elicit responses leading to the emission of other sub- 

 stances which pass into the circulation and thus reach 

 and influence organs which are correlated in action 

 with the muscles directly involved. We have here all 

 the elements of a reflex system — the pituitar}' ser\-ing 

 as a chief centre or hormone-brain. In acromegaly 

 the disordered condition of the pituitary leads to a 

 flooding of the body with adaptative hormones after 

 the most trivial of muscular actions, and hence its un- 

 regulated growth. 



Barwell's Disorder. 



In the Museum of Charing Cross Hospital, Huxley's 

 old school, there is the skull of a boy which shows a 

 very instructive disorder of growth. It is not a unique 

 specimen ; many cases of an exactly similar kind are 

 known. The boy came into the hospital for treatment 

 of a tumour-like swelling of the face, for which Mr. 

 Barwell tied the right carotid artery. The boy died, 

 and it was found that, on the right side of his skull, 

 all those structures which are concerned in mastication, 

 and only the structures concerned in this function, were 

 greatly and uniformly hypertrophicd. The condition 

 was clearly produced long before birth, for all the teeth, 

 including those of the milk dentition, were nearly twice 

 the normal size on the right side of the mouth. So 

 were the jaws and all the bony struts of the face which 



