The Respiratory Process in Muscle. 



453 



temperature had been brought to the freezing point, by which the status in 

 quo could be maintained. 



The first qualitative estimations that were undertaken showed at the first 

 attempt that fatigued muscle contained more lactic acid than resting muscle, 

 and that fatigued muscle after resting in an oxygen atmosphere subsequently 

 contained less lactic acid — a result which was confidently expected in view of 

 the experiments which have been described already. 



Attempts were then made to improve the technical methods for the 

 accurate quantitative estimation of small quantities of lactic acid under the 

 required conditions. In the end, and after trial of alternatives, resort was 

 had to the old method of estimation by weight of the zinc salt obtained from 

 the dextro-rotatory acid which muscle yields, and in the details of this method 

 certain improvements were effected. 



The chief facts relating to the production of lactic acid in the muscle 

 substance, as these have been -determined by our estimations, may be shortly 

 stated. 



Mechanical injury, like that of chopping up the muscle, produces a rapid 

 increase of lactic acid. This rate of production is accelerated by rise of 

 temperature, and is brought to a standstill at the freezing point. 



Isolated undamaged muscle left at rest in air at ordinary temperatures 

 continues to yield lactic acid, so that the total acidity progressively and 

 steadily increases for many hours. Outward signs of this acid production 

 are found in visible physical changes of the muscle, as shortening, stiffening, 

 and loss of translucency, and it is accompanied by a corresponding yield 

 of carbon dioxide previously held in the muscle, but now expelled by the 

 increasing acid. 



As the temperature increases, this spontaneous yield of lactic acid is 

 accelerated. Between 35° C. and 40° C. it is very rapid and reaches a 

 maximum almost instantaneously. This is the "acid maximum" formerly 

 described by Eanke. Nevertheless, if the muscle be rapidly scalded, the 

 source of lactic acid is " fixed," and little or no acid production takes place, as 

 du Bois lieymond formerly showed. 



If the muscle be left at room temperatures in nitrogen or other anaerobic 

 atmospheres, it yields lactic acid at a uniform rate determined by the 

 temperature, and so approaches and finally reaches the acid maximum. It 

 reaches it, however, faster than it does in air at the same temperature. In 

 oxygen, on the other hand, it is found to accumulate no lactic acid at all 

 during many hours or indeed during days at room temperatures. 



Upon stimulation an increase of lactic acid is found. This had been known 

 of course from du Bois Pveymond's time, but the fact had been repeatedly 



vol. lxxxix. — b. 2 p 



