246 MR. MORLEY ROBERTS ON THE FUNCTION OF 



blood clots iu layers, and it is therefore all the more interesting 

 to note that in the embryo the columnce carnece and chordce 

 appear to rise from a spongy network which at an early age fills 

 the primary ventricle. Such origin is strongly suggestive of 

 some process analogou.s to blood clotting or to an iri-itative 

 reaction of the embryonic ventricular wall. The evolutionary 

 dilatation sacs which I suggest were originally pathological can 

 be seen in the embryo during the process of their formation. 

 The path laid down by pathology is trodder by physiology. It 

 follows that during evolution there must have been an immense 

 destruction of organisms whose circulating canals did not react 

 and numbers which retained their unaltei'ed "specific ''characters. 

 The same process goes on to-day. Though many die of cardiac 

 disease, it may be that much youthful functional trouble and 

 •even more serious adult disorders are even now remoulding the 

 heart. No organ is perfect : if it does not degenerate it pro- 

 gresses. Though such processes are " disease," it by no means 

 follows that they will hQ destructive, any more than that the 

 functional incapacity of the tricuspid valves in athletes, Avhich 

 probably precedes what is known as "second wind," is anything 

 now but a cardiac safety-valve. 



As we learn more of the heart and its latent capacities we 

 may perhaps say with the late Dr. H. G. Sutton, "we trust 

 nature too little, to say the least of it." But there are, of course, 

 great difficulties to overcome before we can hope to understand 

 how the cardiac musculature has altered and may still be 

 changing by the addition of new fibres. As yet, little is known 

 of myogenesis. Like a neurone, a muscle cell seems to last a 

 life-time, and though both may degenerate or die, neither pro- 

 liferates after the early period of development. But whatever 

 their histogenesis, new fibres do appear in evolution. Harvey 

 did not refuse to believe in the validity of his own conclusions 

 because he lived before Leeuwenhoek. With considerable hesi- 

 tation I ventui-e to suggest that morphogenetic stress is at its 

 height during foetal development. The child in totero has not, 

 perhaps, the calm and happy life commonly attributed to it. On 

 the contrary, it probably leads a sti-enuous existence, and if it 

 inherits a new weakness this is shown just where and when new 

 stresses find plastic embxyonic tissues to respond to them. If 

 such a speculation is sound it accounts for many phenomena. 

 But in any case, whatever the machinery of inheritance and 

 evolutionary repair, it is certain that new fibres arise where they 

 are needed. 



If svxch views in any way represent the biological history of 

 the heart, it is obvious that many of the opinions of variation 

 usually held are without foundation. Every variation. is definitely 

 caused ; it is in no sense accidental or spontaneous ; it may not 

 be even at once advantageous to the individual : on the contrary, 

 it may be a severe handicap which puts greater general stress on 



