14 THE PRESIDENTIAL ADDRESS. 



protected, and their manoeuvres timed ? Experimental embryologists 

 have begun to explore and discover the machinery of regulation. We 

 know enough to realise that it will take many generations of investigators 

 to work over the great and new field which is thus opening up. When 

 this is done we shall be in a better position to discuss the cause of ' varia- 

 tion ' and the machinery of Evolution. 



If we know only a little concerning the system of government which 

 prevails in the developing embryo we can claim that the system which 

 The Machinery prevails in the growing body, as it passes from infancy to 

 of Growth. maturity, is becoming better known to us every year. The 

 influence of the sex glands on the growth of the body has been known since 

 ancient times ; their removal in youth leads to a transformation in the 

 growth of every part of the body, altering at the same time the reactions 

 and temperament of the brain. In more recent years medical men have 

 observed that characteristic alterations in the appearance and constitution of 

 the human body can be produced by the action of other glands — the pitui- 

 tary, thyroid, parathyroid, and adrenals. Under the disorderly action of 

 one or other of these glands individuals may, in the course of a few years, 

 take on so changed an appearance that the differences between them and 

 their fellows become as great as, or even greater than, those which separate 

 one race of mankind from another. The physical characters which are 

 thus altered are just those which mark one race off from another. How 

 such effects are produced we did not know until 1904, when the late 

 Prof. E. H. Starling, a leader amongst the great physiologists of our time, 

 laid bare an ancient and fundamental law in the living animal body — his 

 law of hormones. I have pictured the body of a growing child as an 

 immense society made up of myriads of microscopic living units, ever 

 increasing in numbers. One of the ways — probably the oldest and most 

 important way — in which the activities of the communities of the body 

 are co-ordinated and regulated is by the postal system discovered by 

 Starling, wherein the missives are hormones — chemical substances in 

 ultra-microscopic amounts, despatched from one community to another 

 in the circulating blood. Clearly the discovery of this ancient and 

 intricate system opens up fresh vistas to the student of Man's evolution. 

 How Darwin would have welcomed this discovery ! It would have given 

 him a rational explanation to so many of his unsolved puzzles, including 

 that of ' correlated variations.' Nor can I in this connection forbear to 

 mention the name of one who presided so ably over the affairs of this 



