78 THYSIOLOGY OF MUSCLES AND NERVES. 



the greatest amount of warmth during tetanus, during 

 wliich no apparent labour is accomplished. The whole 

 internal work of the muscle is in this case transformed 

 into warmth, thus raising the temperature of the muscle- 

 substance ; and the amount of this warmth may, as we 

 have seen, be at least approximately measured and 

 calculated. 



3. One result of the chemical changes which occur 

 within the muscle during its activity, is naturally 

 that part of the constituent matter of the muscle is 

 expended, other matter being deposited in its place. 

 As long as the muscle remains uninjured within the 

 body of the animal, part of the matter thus formed is 

 carried away, and fresh nutritive matter is brought to 

 replace the expended material. The products which 

 arise by decomposition during the activity of the 

 muscle may therefore be indicated in the blood of the 

 animal, and from the blood they are removed from out 

 of the body by special excretory organs. Accordingly 

 we find that the amount of carbonic acid excreted is 

 considerably increased by muscular labour, and that 

 the other products of muscular decomposition, such as 

 creatin and the urea arising from the latter, lactic acid, 

 &c., reappear in the urine. The more abundantly 

 the blood-current flows through the muscles, the more 

 quickly are the products of decomposition removed 

 from the muscle. This is of course possible only in a 

 very inferior degree when the muscle has been cut out 

 from the body. This is the reason why an extracted 

 muscle retains its power of activity for but a very short 

 time. If, for instance, such a muscle is continuously 

 tetanised, it will be found that the contraction, though 

 it is at first very considerable, very soon decreases and 



