STANDARD BASAL METABOLISM CONSTANTS. 225 



was in the pathological state. Such a course is, however, obviously 

 impracticable in the vast majority of instances, since the duties or 

 inclinations of the former patient may preclude periods of study sub- 

 sequent to those made during confinement in a hospital. Furthermore, 

 subsequent to a period of severe illness, there is no assurance in any 

 single period of determinations that the subject has returned, or 

 indeed that he ever will return, to the normal condition, or at least 

 to the condition antecedent to the disease. Finally, because of the 

 great variations in basal metabolism from individual to individual, 

 or under experimentally controllable conditions within the same indi- 

 vidual, single comparisons have little crucial value as a basis for 

 generalization concerning the influence of special conditions on metab- 

 olism unless the influence be very great. 



Practically, therefore, one is reduced in the great majority of cases, 

 and especially in those of the greatest medical interest, to the statis- 

 tical method of comparing observations on a group of individuals of a 

 special class (the metabolism of which is being investigated) with those 

 on individuals which do not possess the characteristics under considera- 

 tion, or with "normal" individuals. 



In experimental work there are two ways in which control constants 

 maybe determined : (1) The control observations may be made simul- 

 taneously with those on the individuals of the special class under 

 investigation. This method is necessarily followed when it is impossible 

 to regulate external conditions with exactness and when individuals 

 which are exactly comparable except for the particular characteristics 

 under investigation must be employed for example, in cases in which 

 two mammals from the same litter, two groups of birds from the same 

 clutch, or two lots of seedlings from the same parent plant must be 

 utilized. (2) Standard determinations may be used as a basis of com- 

 parison for all special groups. This method may be followed in cases 

 in which it is impossible to obtain for simultaneous observation indi- 

 viduals which are more nearly alike than those which can be obtained 

 at other times, and in which the experimental technique is so highly 

 perfected that there is no question but that measurements made at 

 different times or by different observers are comparable within the 

 limits of a very slight physical experimental error. 



In work on metabolism the second method is not merely justified 

 but necessary. The justification for the establishment of a standard 

 control series instead of making normal control measurements for each 

 pathological case lies in the fact that respiration chambers, calorimeters 

 and other apparatus and technique essential for investigating basal 

 metabolism have been brought to such a stage of perfection that, with 

 proper chemical and physical standardizations at frequent intervals, 

 technical errors may be disregarded. Furthermore, subjects upon 

 whom basal metabolism determinations are made must comply so 



