i GENERAL PHYSIOLOGY OF MUSCLE 45 



to the process by which the proteoses and peptones are regenerated 

 into protein by the intestinal epithelium, and the auiino-acids 

 (which are the final products of the digestive decomposition of the 

 proteins) restore and build up the tissues, after being reabsorbed 

 into the lymph and blood. So that muscular proteolysis, which 

 is stimulated or increased by work, in its turn promotes the 

 genesis of protein and consequently the quantity of nitrogenous 

 products in the urine does not materially increase during work. 



This hypothesis appears to us acceptable in view of recent 

 researches on the complex structure of the proteins which build 

 up living matter, and the different cleavage products that can be 

 isolated by the action of enzymes. Pick's studies (1899) on the 

 proteolytic products into which fibrin can split under the action 

 of pepsin are of first importance. Of these products he was able 

 to isolate : 



(a) A proteoalbumose, which contains no carbohydrate group, but 

 has much tyrosine and indole, gives off no glycocoll among its 

 decomposition products, and holds sulphur only in unstable 

 equilibrium. 



(6) A heteroalbumose, which contains no carbohydrate group 

 and hardly any tyrosine and indole, is rich in leucine, with some 

 glycocoll, and holds sulphur only in unstable combination. 



(c) A deuteroalbumose, which contains no carbohydrates. 



(d) Two deuteroalbuminoses rich in carbohydrates. 



(e) Two peptones containing carbohydrates. 



The importance of these results consists in the fact that it is 

 comparatively easy to separate the protein molecule from the 

 carbo-hydrate group (which is oxidised during muscular work) 

 without loss of the fundamental chemical properties of the pro- 

 teins, which therefore retain their capacity for synthetic regenera- 

 tion into protein under the influence of the anabolic activity of 

 the living tissue -cells. If we admit an anabolic proteogenic 

 activity in the intestinal epithelium, it seems reasonable also to 

 assume that it exists in muscle (Vol. II. p. 328). 



IX. We have said that muscular contraction is the most 

 classical and hence the best investigated instance of an explosive 

 discharge of energy in the living world. The potential chemical 

 energy stored up in the muscle is converted during excitation 

 into kinetic energy, which appears in the forms of mechanical 

 work, heat, and electricity, each of which must be considered 

 separately. 



The work done by muscle is measured by the product of the 

 weight raised by the muscle into the height to which it is raised, 

 w x h. If, therefore, the muscle contracts without lifting a weight 

 or overcoming any resistance, it performs no mechanical work. 

 This supposition is, however, purely theoretical since the muscle 

 always has to carry its own weight, which may indeed be reduced 



