6o6 Wm. E. K ell icon 



muscular contraction show that the efficiency of a muscle depends 

 after all fully as much upon the activity of the nerve centers con- 

 trolling it as upon the characteristics of the muscle itself. The 

 coefficients of variability of strength of pull, squeeze of hand, etc., 

 are measures of the variability of the central nervous system as 

 much as of the muscles involved in the action. And when we come 

 to consider the action of absorbmg surfaces or secreting organs it 

 is simply impossible with our present knowledge and technique 

 to make any more than the most general statements about the 

 relation between the size of such organs and their functional value 

 or efficiency. 



One farther consideration suggested above bears directly upon 

 this matter. It is well known that the action of the central nerv- 

 ous system determines to a very considerable extent both the 

 quantitative and qualitative results of the action of metabolizing 

 organs. The functional activity of the digestive glands for exam- 

 ple, is thus constantly modified without there being any detectible 

 physical alteration (Pawlow and others), both the nature and 

 amount of their secretions depending upon the action of the 

 nervous system. The accurate adjustments of variations in the 

 activty of these organs depend not upon the physical characters of 

 the glands but upon the modifying influence of the nervous system 

 in producing slight modifications of their internal metabolic proc- 

 esses. This of course is a factor entirely lacking when the effi- 

 ciency of an organ is directly dependent upon its relatively fixed 

 dimensions. 



We must conclude therefore that measurements of the mass and 

 dimensions of internal organs give data which can be used in an 

 exact study only of these organs themselves without reference to 

 their functional value to the organism as a whole: that they do not 

 furnish evidence as to the precise efficiency of the organs, nor as to 

 the effects of natural or other form of selection upon them in their 

 functional relation; in this respect such data have only a general, 

 not a precise, significance. 



The extremely high degree of variability of visceral characters 

 may then, it seems to me, be also in some part the result of a fact 

 that lies at the basis of many of the practices of modern surgery, 



