346 PHYSIOLOGICAL EEGULATIONS 



oxygen and in carbon dioxide, over diverse ranges of tension, had 

 to be found by measurement. If community of path were a com- 

 plete epitome of physiological study of outputs, the individuality 

 of eliminations of each component would be ignored. Instead, it is 

 now observed that means are available of adjusting several single 

 components without interfering beyond a limited small amount with 

 other components that exchange through the same path. 



In brief, the maintenance of oxygen tensions in diverse tissues 

 of the human body is the equivalent of keeping the body's oxygen 

 content constant. Deficits of a few milligrams of oxygen do not 

 persist when recovery is possible, and payment of oxygen debt is 

 a process rivalled in velocity of exchange of substance only by 

 removal of carbon dioxide excess. Paths of exchange for both are 

 pulmonary, as though this path is capable of faster exchanges 

 (relative to load) than any other. For oxygen the faster recovery 

 is in deficits, for carbon dioxide the faster recovery is in excesses ; 

 and much may be inferred concerning the appropriateness of each 

 of those modifications. 



§ 122. Lactate in man 



Deficit of oxygen is at the present day considered to be in close 

 connection with excess of lactate. By no means all types of oxygen 

 shortage are accompanied by measurable lactate accumulation, and 

 the relations found in physical exercise might equally be considered 

 an exceptional type of oxygen deficit, rather than the rule. 



Lactate may be injected by vein, and the recovery thereafter 

 may be followed by the usual technique of tolerance curves (fig. 

 173). In man no measurements of lactate content of the whole 

 body at the several times appear feasible; hence the procedure 

 (already used in glucose equilibration) is followed of ascertaining 

 the concentrations of lactate in whole blood. In the recovery 

 almost no lactate is excreted; and one-fifth or less of the amount 

 administered is represented by extra consumption of oxygen. The 

 remainder seems to be transformed into other sorts of carbo- 

 hydrate. 



What the relation may be, at various times during recovery, 

 between concentration of lactate in blood and content of lactate in 

 the body as a whole, is open to surmise. One guess is (Margaria et 

 al., '35) that if equilibrium were established, the volume of distribu- 

 tion would be constant at 90% of Bq. Figure 173 does not support 

 this estimate in that type of load. 



