1210 PHYSIOLOGY 



the alveoli and in the arterial blood is rather above than below 

 normal. 



In certain experiments Zuntz and Geppert found that during 

 muscular exercise the respiratory movements were increased to such 

 an extent as to bring the tension of carbon dioxide in the arterial 

 blood below normal. In these experiments the muscular contractions 

 were produced by tetanising, through the spinal cord, the lower limbs 

 of an animal. Under these circumstances the activity of the muscle 

 would be associated with a diminished blood-flow, so that the contrac- 

 tions would be carried out in the absence of a sufficient supply of 

 oxygen. In the absence of sufficient oxygen muscular contractions 

 result in the production, not of carbon dioxide, but of lactic acid, and 

 it is highly probable that in the experiments in question there was 

 a discharge of acid substances into the blood, diminishing the alka- 

 linity of this fluid and therefore lowering its carrying power for carbon 

 dioxide. As a matter of fact, one can produce dyspnoea by diminish- 

 ing the alkalinity of the blood by the injection of acids, and attacks 

 of dyspnoea are observed in the later stages of diabetes, when the 

 alkalinity of the blood is decreased in consequence of the production 

 of such bodies as oxy butyric acid. This dyspnoea has been ascribed 

 to the fact that a diminished carrying power of the blood for carbon 

 dioxide will raise the tension of this gas in the tissues where it is 

 formed, so that a diminished alkalinity of the blood may cause a 

 higher tension of carbon dioxide around the respiratory centre. It 

 has been shown by Ryffel that even a short period of sufficiently violent 

 muscular exercise, i.e. one giving rise to dyspnoea, causes a subsequent 

 increase of lactic acid in the urine, and that the blood itself at the 

 close of the period of exercise contains a demonstrable amount of 

 this acid. Thus in one case the urine, passed thirty minutes after 

 running one-third of a mile in two minutes, contained 454 mg. 

 lactic acid as against a normal excretion of between 3 and 4 mg. 

 of lactic acid per hour. In another experiment blood was obtained 

 from the fore-arm before exercise, immediately after exercise, and 

 three-quarters of an hour later. The exercise, which consisted of 

 running rapidly, lasted two minutes forty-five seconds. The following 

 Table represents the results obtained : 



Lactic acid 

 per 100 c.c. 



Blood before starting . . . . .12-5 mg. 

 Blood immediately after stopping . . . 70-8 

 Blood 45 minutes later ..... 15-9 



The production of lactic acid during muscular exercise may thus 

 be regarded as a second line of defence for the organism, tending to 

 maintain the increased ventilation of the lungs even when the supply 



