720 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



contracting muscle 10.8 per cent, more carbon dioxide than arterial blood. 

 The amount of oxygen consumed, as may be noticed from these figures, 

 bears no relationship to the amount of carbon dioxide liberated ; whence 

 it follows, as already stated, that the formation of carbon dioxide in a 

 contracting muscle is not a simple process of oxidation, but rather the 

 splitting up of some complex compound. 



During contraction the glycogen of " the muscles becomes reduced, 

 while, on the other hand, there is an increase in the amount of kreatin 

 obtainable from the contracted over that found in the resting muscle. 



The question, What is the source of the carbon dioxide and lactic 

 acid developed by a contracting muscle? may, perhaps, be answered by 

 the statement that they are derived neither from the albuminous nor fatty 

 constituents of the muscle, but from the carbohydrates, especially from 

 the glycogen, which may even entirely disappear during the stage of 

 contraction of a muscle, even although the amount of nitrogenous decom- 

 position products in the muscle is not increased and the amount of fat 

 not diminished. From the greater demand of oxygen by a contracting 

 muscle we find, as a consequence, a greater increase in the supply of the 

 arterial blood furnished to a muscle in contraction. 



When a muscle contracts, its arterioles dilate, more blood passes 

 through the muscle, and, as a consequence, the removal of the increased 

 carbon dioxide formed is facilitated. It would appear from this that 

 the source of muscular force is found, not, as was formerly supposed, in 

 the breaking up of albuminoids, but in the chemical changes occurring 

 in muscle which are evidenced by the breaking up of the carbohydrates. 



This statement may appear contradictory to common experience, 

 which teaches that animals fed with albuminoids do more work than 

 those fed on a diet less rich in albuminoids. Our studies on nutrition 

 have, however, indicated that a large supply of albuminous matter 

 renders possible the use of the larger amount of carbohydrates. This 

 will, perhaps, explain the fact that well-nourished herbivora are able 

 to develop more force than the apparently much more powerful carnivora, 

 and that the activity of muscle does not increase the breaking up of 

 albuminates but increases the elimination of carbon dioxide. The few 

 examples in which muscular work is accompanied by an increased 

 excretion of urea, such, for example, as may be occasionally seen in the 

 horse, are only to be accounted for by the insufficiency of the quantity 

 of carbohydrates administered in the food, this insufficiency necessi- 

 tating a destruction of the proteids for the development of force. 



As might be supposed from the above, every muscular contraction is 

 accompanied by an elevation of temperature. Such a heat production 

 may be determined experimentally by a thermometer, and, in a general 

 way, it may be stated that within certain limits the greater the work 



