CHOOSING PHYSIOLOGICAL VARIABLES 423 



practical classification of it among its fellows. Thus, there were 

 loads (AW, AC), each distinct with respect to component, species, 

 living unit, and other particulars. There were rates of exchange 

 (SW/At, SC/At), each distinct (in addition) with respect to paths of 

 exchange and unit of time involved. There were components, liv- 

 ing units, analyzable tissues, modes of chemical analysis, rates of 

 physiological activity, volumes, concentrations, various ratios. 

 Any quantity that could be adequately defined and classified might 

 appear on the docket of data available. 



Among these data, further choices were made, taking two vari- 

 ables at a time from among those quantities that had been mea- 

 sured simultaneously. The choices were guided by the desire to 

 learn how exchanges are concerned in maintenances of content. At 

 first, loads and rates were correlated; AW was related to SW/At, 

 AC to SC/At. Later, AW was successively related to each of many 

 varieties of AE, AG, AH, etc.; to SC/At, SG/At, SH/At, etc. The 

 variables and the relations among them having been classified, 

 living units were compared within one class of relations after 

 another. 



Without indicating many of its subdivisions, the whole course 

 of the investigation is represented by the following outline : 



Ji. Component Water (and Volume). Chapters II to XIII. 

 Ml. The four variables. Chapters II to IX. 

 Gi. Species Dog. Chapters II to IV. 

 <Pi. Type of loading AW5. § 7 to § 8. 

 Ni. Individuals B. Figures 1 to 6. 



gi. Tolerance diagram. Figures 1 and 4. 

 Pi. Urinary exchanges. Figure 4. 

 P2. Other paths. Figure 15. 

 ^2- Other bi-correlations. Figures 2, 6, 19, 17. 

 N2. Other individuals. Figures 35, etc. 

 (p2- Other types of loading. Chapter III. 

 4)3. Preference among environments. § 20. 

 4)4. Variability. Chapter IV. 

 02. Other species. Chapters V to VII. 

 63. Parts of organisms. Chapter VIII. 

 Ms. Other groups of variables. Chapters X to XII. 

 J2. Other components. Chapters XIV to XVII. 



For certain purposes it would have been valuable to designate 

 the precise type of each content or exchange, thereby different!- 



