340 PHYSIOLOGICAL REGULATIONS 



rates of recovery in steady states of excess of blood glucose might 

 be correlated, complete data for which are available. From other 

 sources, recoveries after single administrations would be repre- 

 sented by a series of ' ' glucose tolerance ' ' tests. For them, a known 

 amount of glucose is suddenly injected into the circulating blood, 

 after which the blood's concentration of sugar is measured at suc- 

 cessive times. Such tests in dogs show that (1) disappearance of 

 glucose is absolutely faster with larger doses, (2) disappearance 

 rates diminish with time and with concomitant decrease of incre- 

 ment, (3) disappearance rates are modified by removal of liver, 

 pancreas, or adrenals, by anesthesia, insulin, phlorizin, renal liga- 

 tion, and numerous other factors (Goldstein et al., '32). 



Many devices have been used to compare glucose tolerance 

 curves. Rates of recession, slopes of return, hyper-glycemic areas, 

 peak effects, and terminal levels, are all of service to the graphi- 

 cally minded. ' ' Insulin sensitivity curves ' ' may equally be termed 

 tolerance curves in glucose deficits, to indicate that they differ in 

 component and sign from tolerance curves for other substances. 

 Finding now that "tolerance tests" are particular instances of 

 recoveries, all the rate and time factors and ratios found useful for 

 water (§ 105) may be applied to glucose. 



Glucose, therefore, exhibits net equilibration of content both in 

 stationary states and temporary states. Excesses are dissipated 

 by several paths, and the proportion lost by each path varies 

 with the load. Deficits and excesses of equal magnitude are re- 

 turned at about the same rates. Promptness of recovery as ex- 

 hibited in tolerance curves in positive and negative loads is matched 

 by the smallness of variabilities of content found in single indi- 

 viduals and in populations. 



§ 120. Caebon DioxroE in man 



Carbon dioxide (plus bicarbonate, etc.) may be thought of as a 

 constituent of the body as a whole. Exchanges of carbon dioxide 

 in mammals represent chiefly losses by elimination through lung 

 alveoli, competing with gains by internal production. Increments 

 in the carbon dioxide content of the body are roughly estimated 

 from the extra carbon dioxide that has been eliminated (a) in 

 forced breathing and (b) in recovery from equilibrium with high 

 tensions of inspired CO2. It is found that 0.2 hour or more is re- 

 quired in man to attain a new stationary content of this substance, 

 the net retention or elimination approaching some asymptote. 



