FUNCTIONAL VARIATION 87 



peculiar action of certain parts possessed by the race in com- 

 mon, but whose special functioning in each particular case 

 determines the place of the individual in the scale of life. 



Variation in vital functions. For present purposes the animal 

 body may be regarded as a colony of organs, each endowed 

 with its own peculiar function, the life of the whole and of 

 every member being dependent upon the degree of success 

 with which each portion does its work. The whole is, therefore, 

 as strong as its weakest member, and when the whole is put to 

 work in service for man, that service will depend not only upon 

 the functional activity of the special organ involved, as the 

 udder or the muscular system, but also upon the successful 

 discharge of all vital functions when subjected to the unnatural 

 strain involved in working under pressure. The point at which 

 the machine will break down or fail to do successful work is, 

 therefore, a matter of relative strength of parts, and in the last 

 analysis the limiting element in performance is not infrequently 

 one or more vital functions, which experience shows are as 

 variable as are other and, from the biological standpoint, less 

 important characters. 



The beat of the heart, in man for example, though steadily 

 decreasing in rapidity from infancy to old age, yet varies be- 

 tween different individuals at maturity all the way from less 

 than fifty to more than eighty beats per minute. Athletes tell 

 us that the slow beat is characteristic of long-distance running 

 and sustained effort generally, but that individuals of this order 

 are ill adapted to short-distance running or other work requiring 

 quick response to stimulus. 



There is a marked difference in the digestive powers of 

 different animals, and some individuals starve because the 

 stomach and intestines are unable to dissolve sufficient food to 

 meet the demands of the body, and there are all degrees of 

 starvation. 1 Others with excellent digestion but with limited 

 powers of assimilation fail to make use of the full supply that 



1 Wide study of men, animals, and plants will reveal many cases in which the 

 individual has accustomed itself to an abnormally small food supply. The effect 

 is not necessarily fatal, but it is shown in reduced output either of labor, body 

 product, or other form of organic activity. 



