1867.] Dr. Parkes on the Elimination of Nitrogen. 



57 



The last 10| hours of tlie two exercise dajs formed a period of rest ; 

 and during this time the excretion increased, and this increase continued 

 more or less for four subsequent days. 



This might be explained by the passing olf of excretory products 

 formed during the contraction, according to the old theory ; but if so, it 

 seems singular that the increased excretion should have been so mode- 

 rate, and at the same time should have been spread over so m^any days, 

 whereas on the hypothesis I have suggested it is easily explicable. 



During the exercise-period the extra action of the muscles had added 

 a large amount of nitrogen to their structure ; at the end of the time 

 the muscles must have been bulkier, and therefore in the succeeding 

 period of rest furnished a larger elimination of nitrogen than in the 

 after rest-period when they were smaller. Moreover, after the exercise- 

 period there was much more rest than after the rest-period. In the 

 first day after the exercise the men were tired and rested the whole day, 

 and even on the following days did not probably make so much exertion 

 as usual. And the gradual elimination for so many days looks much 

 more like a temporarily enlarged organ returning slowly to its normal 

 size, than like the passage of accumulated excretory products ; the chief 

 product being the very soluble urea Avhich is always so rapidly removed 

 from the muscles that scarcely any can be detected in them. 



The facts observed in the experiments on a non-nitrogenous diet 

 seem now to be also easily explained. The decrease in the urea during 

 the period of exercise equally occurred, because the muscles used more 

 nitrogen in their action than in the rest-period, taking it from the store, 

 and thereby no doubt robbing other parts. 



During the two days of exercise without nitrogen, the muscles may 

 have been just as well fed with nitrogen as during the experiments with 

 300 grains, only other parts could not have been so ; other organs and 

 the muscles not called into play must have acquired nitrogen with more 

 difiiculty, and consequently when nitrogen was again given, a largo 

 portion was retained to replenish the store and to feed the organs which 

 had been on short allowance. 



The quantity retained when nitrogen was again given did not serve (we 

 may suppose) to nourish muscles exhausted by the exercise (which on my 

 theory had even increased in nitrogenous constituents), but other parts. 



If this reading of the facts be admitted, it may be asked how it will 

 affect the inference drawn from the experiments of Professors Pick and 

 Wislicenus. They determined the nitrogen discharged, calculated how 

 much muscle it represented, and then argued (and as Dr. Prankland has 

 shown, correctly argued) that this amount of muscle could not have pro- 

 duced the mechanical force which had been exerted. But it is apparent, 

 if I am correct, that the measure of the work must be the amount of 

 nitrogen appropriated by, and not that eliminated from, the muscle, 

 and this was not shown in their celebrated experiments. 



But though doubt may be raised as to the basis of their opinion, I 



