DIVERSE COMPONENTS 349 



crement (load), may be inferred from analyses of one tissue snch 

 as blood. Thus, the content of oxygen might be estimated from 

 arterial oxygen concentration. In the case of heat the exchanges 

 of the whole body were actually so ascertained from local tem- 

 peratures. Several assumptions underlie any such procedures, 

 especially the assumption of a roughly constant volume of distribu- 

 tion of the component under consideration. For exact work it is 

 desirable to study by some independent method the limitations 

 under which this volume is constant or known. One of the most 

 severe limitations is probably time. Any sudden increment itself 

 upsets the relative concentrations among tissues ; and only either 

 by measurement in numerous tissues or by knowledge of the whole 

 load in the body, can the regression of the concentration in the sam- 

 ples with the load of the whole body be ascertained. 



With greater certainty, the rates of exchange and the loads may 

 be kept in terms of concentration of the one tissue sampled. This is 

 what is ordinarily done in the study of glucose ' ' tolerance ' ' in mam- 

 mals. And so it may be done for any conceivable component. It is 

 a procedure available for the study in single individuals of com- 

 ponents that are transformed within the body ; for total exchanges 

 of such components cannot be measured by their elimination alone. 



When, therefore, glucose equilibration was studied from the 

 point of view of the whole organism, the same data were also refer- 

 able to the blood concentration of glucose. I elected to put this 

 component in terms of the whole body in view of the fact that 

 various paths of disposal are measured for the body as a whole. I 

 elected, however, to consider the exchanges of lactate in the blood 

 alone, since disposal was not separately measured, and in spite of 

 the fact that removal of diverse portions of the body from inter- 

 course with the blood is known to modify greatly the rates of ex- 

 change by the blood. 



The definition of components is guided ordinarily by conveni- 

 ence of measurement. Concentrations are very often proportional 

 to contents, and reciprocal to volumes of distribution. Each may 

 receive separate definition on occasion. Glucose, for instance, is 

 more accurately termed "total reduction of X's reagent under pre- 

 scribed conditions of analysis"; for, use of Y's procedure may 

 redefine it. Whether ''combined" substances shall be lumped with 

 ''free" materials in one component is a matter of convenience. 

 Even water is variously fractionated by analytical methods into 



