The Respiratory Process in Muscle. 



455 



the fatigued or dying muscle is placed in oxygen. With a rise of temperature 

 above 30°, however, the accelerated spontaneous production of lactic acid 

 overcomes this oxidative removal ; the muscle enters into heat rigor and 

 develops the acid maximum in spite of the presence of oxygen (fig. 7). 



Hours 12 3 4 5 lO 



Fig. 7. — Lactic acid production and loss, in atmosphere of oxygen at different tempera- 

 tures. Fatigued muscles were used for all. At 30° C. gain in lactic acid is shown : 

 at 15-18° C. the course of loss is followed, x loss of excitability. 



Severe mechanical injury, moreover, produces an acid yield which is 

 unbalanced by oxidative removal, and muscle chopped in pieces or ground up 

 with sand in the presence of oxygen very rapidly reaches the acid maximum, 

 and reaches it apparently as rapidly as if oxygen were absent. It seems that 

 the normal architecture of the muscle is a necessary condition for the 

 oxidative process of removal. 



These results as here stated very shortly, when set side by side with the 

 facts of the carbon dioxide output already given, show clearly again that 

 oxygen does in fact enter the living substance of muscle for the purposes of 

 an immediate oxidation, and not as a preparer or builder up of material 

 ready for explosion. We are now therefore in a position to distinguish more 

 clearly those chemical events in muscle which are anaerobic and independent 

 of oxygen, from those, on the other hand, in which oxygen plays a part. 



Plainly the act of contraction and the process of rigor, each with its accom- 

 paniment of lactic acid formation, are anaerobic functions. Neither of them, it 



2 p 2 



