THE CONTROL OF THE RESPIRATION 369 



TIME AFTER DISCONTINUING ALVEOLAR C0 2 TENSION 



A BRIEF PERIOD OF IN MM. HG 



MUSCULAR EXERCISE 



(Douglas.) 



In this table the figures of Period 1 represent the alveolar C0 2 

 tension in mm. Hg immediately following a period of strenuous work. 

 The figures in Period 2 are for the same individual again performing 

 the same amount of work with, however, only a short period of rest in- 

 tervening, and the figures of the third period are a repetition of the same 

 conditions. It will be observed that the muscular exercise at first raised 

 the alveolar tension of C0 2 from the normal of 39 mm. to 49.2 mm., but 

 that in three minutes after the work had been discontinued the tension 

 was considerably below the normal. During the second period of mus- 

 cular exercise the C0 2 in the alveolar air collected immediately after the 

 effort did not increase above the normal level, and in the third period 

 the increase was still less results which are entirely in conformity with the 

 view that as a consequence of the first period of muscular exercise non- 

 volatile organic acids had accumulated in the blood, so that to produce 

 the required respiratory activity in the second and third periods a 

 much less increase in C0 2 tension was required. 



We may sum up the conclusions which these observations justify by 

 stating that during muscular exercise the C H of the blood becomes slightly 

 increased because of the liberation into it of C0 2 and of lactic acid from 

 the acting muscles. The respiratory center is, however, so sensitive to 

 the slightest increase in C H that it immediately responds and produces 

 hyperpnea, with the result that the volatile C0 2 is so washed out of the 

 blood that the C H is held down in spite of the continued production of 

 acid substances by the muscles. The more strenuous the exercise, the 

 less able is the 2 content of the blood to keep pace with the metabolic 

 activity of the muscles, so that relatively more and more lactic acid is 

 produced, necessitating therefore a greater and greater washing out 

 of C0 2 . 



