CHAP. IX.] THE CONTRACTILE TISSUES. 387 



Expert- Voit 1 seems to have been the first to examine very 



mentsof Volt, carefully this question of the influence of exertion upon 

 nitrogenous excreta. He selected the dog, as being better fitted for 

 the conditions of rigorous experiment than men, who had been 

 previously observed. The dog underwent severe exertion under two 

 sets of conditions : (1) when fasting from all food except water, and (2) 

 when on a diet just enough to cover all loss of weight when no work 

 was done. In each set of conditions the average excretions of resting 

 days and working days were compared. Sometimes resting days and 

 working days alternated ; but usually two or three days in succession 

 were devoted to rest, and two or three to labour. In this way there 

 was less danger of urine being retained in the bladder over the period 

 of a working day and expelled during the following resting day. In 

 all the experiments the dog was allowed to drink as much water as 

 he desired. Work was done in turning a tread-wheel, the number of 

 turns being registered, and the work carefully calculated. The dog 

 was taught to drive the wheel with great rapidity, encouraged by his 

 master's voice; and it was found that 10 minutes at a time was 

 sufficient to thoroughly fatigue the animal. A working day consisted 

 of about six periods, of 10 minutes each, spent in the wheel, with 

 about an hour's rest between each period. The greatest care was 

 taken to obviate loss of excretions ; thus the dog was taught to 

 micturate at a given spot and at regular intervals. The weight of the 

 dog, the water ingested, the urine, the urea, and the faeces were all 

 carefully determined from day to day. The dog weighed about 33 

 kilograms. 



A studv of Volt's data conclusively shews us that 

 Conclusions. . . ( , J , ., . . J . ,, 



during tne days ot exertion the excretion ot urea is 



increased ; but it discovers also that, 



1. The increase is absolutely very small; viz. an increase of 

 about 1 5 grams in the fasting experiments when the excretion 

 of repose was 10 15 grams a day ; and an increase of 5 10 grams 

 in the experiments with food, when the excretion of repose was about 

 110 grams a day. 



2. The increase has no constant relationship to the work done. 



3. The increase is evidently more influenced by the diet (viz. by 

 the amount of water ingested; by the fact of food being taken; &c.) 

 than by the circumstance of work. 



Volt's dis- Impressed by the smallness of the increase of nitro- 



cussion of Ms genous excreta during severe labour, Voit endeavoured 

 experiments. ^0 discredit the inference that some part of it, however 

 small, is directly owing to the activity of muscles. He dwelt upon 

 the circumstance that the free mgestion of water is, of itself, enough 

 to raise the excretion of urea by the urine. He pointed out that the 



1 C. Voit, UntersuchungeniL denEinfluss des Kochsalzes t des Kaffce's undder Muskel- 

 bewcgungen auf den Stqffwechsel. Mimchen, 1860. 



25-2 



