PRESIDENTIAL ADDRESS. 281 



to them from the central nervous system ; they throw a hormone — adrenalin — 

 into tile circulating blood, which has a double eftect ; adrenalin acts on the flood- 

 gates of the circulation, so that the major supply of blood passes to the muscles. 

 At the same time it so acts on the liver that the blood circulating through that 

 great organ Becomes laden with blood-sugar. We here obtain a glimpse of the 

 neat and effective manner in which hormones are utilised in the economy of the 

 living body. From that glimpse we seem to obtain a clue to that remarkable 

 disorder of growth in the human body kno\^■^l as acromegaly. It is a patho- 

 logical manifestation of an adaptational mechanism with which we are all 

 familiar. Nothing is better known to us than that our bodies respond to the 

 burden they are made to bear. Our muscles increase in size and strength the 

 more we use them; increase in the size of our muscles would be useless unless 

 our bones also were strengthened to a corresponding degree. A greater blood 

 supply is required to feed them, and hence the power of the heart has to be 

 augmented ; more oxj'gen is needed for their consumption, and hence the lung 

 capacity has to be increased ; more fuel is required — hence the whole digestive 

 and assimilative systems have to undergo a hypertrophy, including the apparatus 

 of mastication. Such a power of co-ordinated response on the part of all of the 

 organs of the body to meet the needs of athletic training presupposes a co- 

 ordinating mechanism. We have always regarded such a power of response as 

 an inherent property of the living body, but in the light of our growing know- 

 ledge it is clear that we are here dealing with a hormonic mechanism, one in 

 which the pituitary gland is primarily concerned. When we study the structural 

 changes which take place in the first phase of acromegaly,' we find that not 

 only are the bones enlarged and overgrown in a peculiar way, but so are the 

 muscles, the heart, the lungs, the organs of digestion, particidarly the jaws ; 

 hence the marked changes in the face, for the form of the face is determined 

 by the development of the upper and lower jaws. The rational interpretation 

 of acromegaly is that it is a pathological disorder of the mechanism of adapta- 

 tional response; in the healthy body the pituitary is throwing into the circula- 

 tion just a sufficiency of a gro^wth-regulating substance to sensitise muscles, 

 bones, and other structures to give a normal response to the burden thrown on 

 the body. But in acromegaly the body is so flooded with this substance that 

 its tissues become hypersensitive and respond by overgrowth to efforts and move- 

 ments of the slightest degree. It is not too much to expect, when we see how 

 the body and features become transformed at the onset of acromegaly. that_ a 

 fuller knowledge of these growth mechanisms will give us a clue to the prin- 

 ciples of race differentiation. 



There must be many other mechanisms regulated by hormones with which 

 we are as yet totally unacquainted. I will cite only one instance — that concerned 

 in regulating the temperature of the body. We know that the thyroid and also 

 the suprarenal glands are concerined in this mechanism ; they have also to do with 

 the deposition and absorption of pigment in the skin, which must be part of the 

 heat-regulating mechanism. It is along such a path of inquiry that we expect 

 to discover a clue to the question of race colour. 



This is not the first occasion on which the doctrine of hormones has been 

 applied to biolocical problems at the British Association. In his Presidential 

 address to the Zoological Section at Sheffield in 1910 Professor G. C. Bourne 

 applied the theory to the problems of evolution : its bearing was examined in 

 more detail in an address to the same section by Professor Arthur Dendy during 

 the meeting at Portsmouth in 1911. At the meeting of the Association at New- 

 castle in 1916 Professor MacBride devoted part of his address to the morpho- 

 genetic bearings of hormones. Very soon after Starling formulated the hormone 

 theory. Dr. J. T. Cunningham applietl it to exnlain the phenomena of heredity.' 

 Nay, rightly conceived, Darwin's theory of Pan-genesis is very much of the 

 same character as the modern theory of hormones. 



« See Keith, Lancet. 1911. ii.. p. 993; 1913, i., p. 305. 



' Dr. J. T. Cunningham, Proc. Zoo. Soc. London, 1908. p. 434. 



