PATHOLOGICAL STATES IN EVOLUTION. 



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all who experience it, though such stresses fall short of those 

 which cause death. Variations of this order may only be 

 advantageous to the whole species as a continuing race. They 

 may destroy, and doubtless have destroyed, individuals without 

 number at an earlier age than the usual life-period of the 

 * unvaried type. We may possibly imagine a part of humanity, 

 now responding to stresses which make the heart do more work 

 • and fail earlier, displaying such energy during their shorter 



life as to displace those with a normal cardiac mechanism which 

 survives to the average age of man. It is to be inferred from 

 these considerations that the structure of an organism is not a 

 congeries of minute fortuitous advantageous variations, nor the 

 gradual massing of details in an orthogenetic line, nor the result 

 of large discontinuous variations due to chromosomatic in- 

 heritance, but a complex of definite reactions to definite stresses. 

 The true theory of living structure is that its growth is neither 

 casual nor foreseen, but that is what we may call, in political 

 language, the " opportunism " of the organism as a whole. Every 

 advance is a forced, even a desperate, experiment. Life, like a 

 hypothesis or a clam, is built up by stopping leaks. 



The evolution of the stomach seems to have followed the 

 lines suggested for cardiac development. From the physiological 

 point of view, a, straight intestinal tube which becomes dilated 

 cannot be considered anything but pathological. It has failed 

 under the stresses imposed on it, but the organism which 

 reacted turned a weak dilatation sac into a strong perma- 

 nent food pouch. The results to the reacting organisms were 

 many. The ingested food became temporarily static, was more 

 thoroughly dealt with, and the organism was not continually 

 feeding. Its whole available energy was not devoted to nutrition : 

 it had time at its disposal and could develop other functions 

 leading to further structures. That the human stomach is such 

 an organized failure is suggested forcibly by the musculature. In 

 the small intestine this is composed of two layers of fibres, 

 circular and longitudinal. In the stomach it is made of three 

 sets, an inmost layer of oblique fibres being added. This oblique 

 layer is obviously a later growth and, as would be expected on 

 the lines laid down as to disaster and repair, its strongest fibres 

 are found just where they are wanted, that is, supporting the 

 greater curvature or dilatation of the stomach. This later 

 layer is naturally less well developed than the longitudinal and 

 circular fibres. Other oblique fibres are formed about the pylorus 

 where they form the sphincter. I suggest that these oblique 

 muscle fibres arose as points of strain, under intense stimulation. 

 The dilated pouch has reacted in accordance with mechanical 

 law, just as the heart did with its more complex arrangement of 

 oblique fibres' woven into a structure capable of giving in the 

 left ventricle a thrust of over fifty pounds. The reacting organism 

 is no fool of a mechanic either in its bones or its muscles, and 



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