46 CM. JACKSON 



to change in correlation with age. Coefficients of correlation in 

 different organs at the same age may be compared with each other, 

 however, since the body weights and the 'spurious correlation' 

 factor would be the same for all. 



The coefficient of variation of the relative or percentage weight 

 is usually much lower than that of the absolute weight of the 

 various organs.^ The difference is inconstant, however, and the 

 eyeballs form a marked exception to the rule. In most cases, 

 therefore, the percentage weight of an organ can be predicted 

 much more accurately than the absolute weight of the organ at 

 any given age. The data agree in general with the theory that 

 the growth of the individual organs is correlated with the growth 

 of the whole body more closely than with age, as Donaldson 

 ('08) has found for the brain of the rat. 



For comparison of the variability in the human viscera, a few 

 data are available. Pearson ('97) from data of Reid and Peacock 

 calculates the coefficients of variation for the human heart (abso- 

 lute weight), male, 19.8, female, 20.7; liver, male, 14.5, female, 

 22.2; kidneys, male, 20.5, female, 22.5. Greenwood ('04) from 

 more extensive data finds the coefficients of variation for healthy 

 organs (males only) approximately as follows: heart, 17.7; liver, 

 14.8; kidneys, 16.8; spleen, 38. From the foregoing it would 

 therefore appear that the heart, liver and kidneys are less variable 

 in man than in the rat. The spleen is more nearly alike in the 

 two forms, and in both is by far the most variable of the organs 

 compared. Pearl ('05) classifies the human bodily characters 

 with reference to variability in three groups: (1) those with 

 coefficient of variation above 10, viscera in general, whose weight 

 depends largely upon the general metabolic condition of the body 

 and in which natural selection is concerned with functional ability 

 rather than with size: (2) those below 7, chiefly skeletal dimen- 

 sions, in which the conditions of (1) are reversed; and (3) those 

 with coefficient from 7 to 10, including brain and skull capacity, 

 in which intermediate conditions are found. 



' Chisolm ('11) finds the coefficient of variation for the percentage weights in 

 adult rabbits, for the spleen, 46.7; kidneys, 16.5; liver, 32.5 This would indicate 

 that these organs are more variable in the rabbit than in the albino rat. 



