436 



THE RESPIRATION 



isolated muscle. These observers found that lactic acid is produced in excised muscles 

 only when the muscular contraction occurs in a deficiency of O . When it occurs in 

 an adequate supply of O t> , CO 2 instead of lactic acid is produced. 



Much light has been thrown on the physiology of muscular exercise 

 by studying the alveolar C0 2 tension and the respiratory quotient. The 

 results of such observations are given in the accompanying table. 



In the first column is given the 2 used in c.c. per minute. Among other 

 things these figures indicate the actual amount of work done. In the 

 second column is given the C0 2 production in c.c. per minute. By divid- 

 ing the figures of the second column by those of the first, we obtain the 

 figures of the third column, representing the respiratory quotient. The 

 fourth column gives the C0 2 content of the alveolar air, and the last 

 column the total alveolar ventilation in liters per minute. 



Taking for the present the figures in the first and fourth columns it will 

 be noted that, as the muscular work increases up to a total consumption of 

 about 1600 c.c. of 2 per minute, the C0 2 percentage in the alveolar air 

 steadily increases. The question arises, does the alveolar ventilation 

 increase in proportion to the increase in C0 2 tension? If it does so, 

 increase in C0 2 tension in the blood can be held solely responsible for 

 the hyperpnea (i. e., a pure C0 2 acidosis) ; whereas if the hyperpnea is 

 greater than can be accounted for by the increase in C0 2 tension, other 

 factors must be acting to excite the respiratory center. By making this 

 same individual breathe atmospheres containing different percentages of 

 C0 2 it -was found that to produce a doubling of the alveolar ventilation it 

 required an increase amounting to 0.33 per cent of an atmosphere of CO., 

 in the alveolar air (see also page 366). When we examine the above 

 figures during muscular exercise, however, we find that a rise in alveolar 

 C0 2 from 5.70 to 6.36 (i. e., 0.66 per cent) caused the alveolar ventilation 

 to increase by considerably more than four times, whereas had it been 



