90 WARFARE IN THE HUMAN BODY 



same causes that the pathologist can demonstrate to be 

 working at the present day. Only such organisms as 

 respond by direct reactions in a manner that finally turns 

 out to be useful, or at the very least compatible with life 

 and reproduction, are able to survive. The whole of 

 growth and development thus becomes largely a function 

 of effective morphogenetic repair to organic failure and 

 disease. 



Though this is not the place to deal at length with the 

 vexed question of transmission of modifications, it may 

 be remarked that the foregoing arguments seem to imply 

 that such alterations, as a matter of fact, are inherited. I 

 think some progress can be made if we simply assume 

 provisionally that organisms do tend to repeat them- 

 selves, and that it is unlikeness rather than likeness which 

 requires explanation. We know that gross unlikeness is 

 almost always due to a lack or excess of some internal 

 secretion, hormone, or enzyme, and from this it may be 

 inferred that likeness is due to such catalytic machinery 

 coming over in the zygote, and to each differentiation 

 producing anew its own peculiar products which stimulate 

 or inhibit further growth and differentiation. Some 

 time ago I was struck by a remark of Starling's, that each 

 new organism seemed a fresh " creation." He gave this 

 up on account of the difficulty he found in the " time 

 element " of the problem ; but I venture to think he was 

 right in his surmise. 1 There is a growing body of opinion 

 in support of this view, as the names of Cunningham, 

 MacBride, Dendy, and Bourne seem to bear witness. We 

 must certainly take into account these hormonic regulators 

 of metabolism, and if we accept the view that hyper- 

 thyroidism is the direct cause of the phenomena seen in 



1 See Chapter VII., Heredity and Environment. 



