] 867.] Dr. Parkes on the Elimination of Nitrogen. 



55 



Both the theories of muscular auction now being discussed by physio- 

 logists seem to me insufficient to account satisfactorily for all the above 

 facts. 



The old theory was, that a muscle was more or less destroyed during 

 action and was repaired during rest, and if so, it seemed reasonable to 

 suppose that the action of the muscles would be measured by the amount 

 of nitrogen eliminated. But the decrease in the nitrogenous excretion 

 during exercise and its very moderate increase afterwards (an increase 

 quite out of proportion to the amount of muscle supposed to be destroyed) 

 seem quite inconsistent with this view. 



The new theory, springing from the experiments of Professors Pick 

 and "Wislicenus, viz., that the nitrogenous framework of a muscle is 

 merely the machinery which allows changes in the non-nitrogenous sub- 

 stances to take place, and that in itself it undergoes during exercise no 

 change, though at first sight consistent with some of the facts, does not 

 appear to be so with all. It does not account for the increase of nitro- 

 genous excretion in rest, for the decrease during exertion, or for the 

 increase afterwards, nor in a satisfactory manner for the great retention 

 of nitrogen in the system which occurs after exercise on a non-nitroge- 

 nous diet. 



There is something more in the facts than either disintegration se, 

 or stability of nitrogenous composition during muscula,r action, will 

 account for. 



We must find some other explanation ; and it appears to me tliat we 

 can only express the facts by saying that a muscle during action appro- 

 priates more nitrogen than it gives off, and during rest gives off* more 

 than it appropriates. "We have, perhaps, strictly speaking, no right to 

 go beyond this ; but it seems clear that as a muscle could hardly be sup- 

 posed to have two siraiiltaneous actions, we may simplify the above ex- 

 pression by stating tha,t during action a muscle takes nitrogen, and 

 during rest gives it off". To put this in other words, the action of a 

 muscle would seem from these experiments not to be connected with 

 disintegration, but with formation ; when it is in exercise the muscle 

 increases, when it is quiescent it lessens in bulk. It may seem a bold 

 innovation to attempt to reverse in this way the old theory of muscular 

 action, especially as the same rule would have to be applied to nutrition 

 generally ; but if it explains all the facts, it is at any rate entitled to be 

 fully considered. 



In applying this expression in the explanation of tlie facts, I must 

 premise that the nitrogen discharged by the kidneys and bowels cannot 

 be supposed to be derived solely from the muscles. As it represents all 

 the nitrogen going in, it must be derived from all the nitrogenous tissues, 

 from the nervous substance, the gland cells, the albuminous membranes 

 and fluids, in fact from all nitrogenous structures. That portion of it 

 which is derived from the muscular system comes only in part from those 



