INTERRELATIONS AMONG COMPONENTS 417 



are not to be attributed to the components represented. He who 

 creates variables in a separate order of independence is one who 

 also terms those variables ''causes." Only by virtue of having 

 tested some variables as if independent, does it appear justified to 

 imagine they are causes. 



Methods of representing many physiological variables are now 

 very primitive, and I hope that more promising ones will be found 

 than the crude diagrams herewith suggested. The organism is 

 apparently not limited in performance by human inadequacy in 

 recording the multitude of its relations. 



(4) Another approach to interactions of physiological proper- 

 ties is as follows. A great variety of loads and conditions might 

 be studied in their interrelations if a measure of "value'' is se- 

 lected. Familiar examples are the commercial yields of agricul- 

 tural crops (Fisher, '37). The monetary value of yields equal in 

 weight varies from time to time with economic situations ; similarly 

 any scale of physiological value varies with the appraiser. Diverse 

 measures of value emphasize man-power, longevity, enjoyment of 

 leisure, meat or milk production, piece work, mental stability, 

 physical fitness, or any other better or worse defined criterion. 

 Medicine and surgery have an almost singular measure of value in 

 the survival and comfort of the patient. 



In Arbeitsphysiologie, to operate machines of certain specifica- 

 tions, measurable muscular forces and energies are expended in 

 particular manners. Physiologists choose criteria as to what are 

 the immediate and ultimate effects of the work upon the human 

 organism. Not content with rate of oxygen consumption, it is 

 usual to measure heart frequency, cardiac output, arterial pres- 

 sures, coordination and speed of movement, reaction times, effects 

 of giving sugar, effects of rest periods, effects of room tempera- 

 tures, and many other ''factors." Multiple indices are devised 

 whereby each measurement and test takes its share in rating the 

 individual. 



Some scientists have a tradition of "varying one factor at a 

 time"; others vary many simultaneously. Those who have con- 

 sidered the matter quantitatively point out that the latter "ar- 

 rangement possesses two advantages over experiments involving 

 only single factors: (i) Greater efficiency . . . and, (ii) Greater 

 comprehensiveness" (Fisher, '37, p. 110). "If the investigator, in 

 these circumstances, confines his attention to any single factor, we 



