FUNCTIONAL VARIATION 8 1 



former and underrate the latter, so prone are we to remember 

 striking and maximum data. 



These are not isolated and peculiar cases. Professor Eraser 

 of the University of Illinois tested 554 cows in 36 commercial 

 dairy herds of the state for a full period of twelve months each. 

 He found that the best 25 per cent of the whole number tested 

 were able to produce an average of 30 1 pounds of butter fat per 

 year, while the 25 per cent of lowest efficiency were able to pro- 

 duce an average of but 133.5 pounds, a range of consid- 

 erably more than two to one. The practical significance of this 

 difference is pointed out by Professor Eraser as follows : If it 

 costs thirty dollars a year to feed the poorer cows and thirty- 

 eight dollars a year to feed the better ones, then at present prices 

 a herd of twenty-five of the latter will produce as much net pro jit 

 as would a thousand of the former. A little calculation will show 

 the immense saving in labor in keeping the smaller herd, and, what 

 is equally significant, the relatively smaller investment in animals, 

 feed, and barns, and the smaller volume of business generally. 



The faculty of producing a high yield of milk manifestly 

 depends not only upon the activity of the mammary glands but 

 also upon the capacity of the stomach to handle a large amount 

 of feed, and the ability of every organ of the body to discharge 

 its normal functions regularly and to endure the wear and tear 

 of sustained exertion under heavy pressure. This particular 

 function of milk production is, therefore, a kind of resultant or 

 algebraic sum of many body functions, and we should not expect 

 to find its maximum except rarely and in few individuals. A 

 simpler function practically independent of others would there- 

 fore be unhampered by their weaknesses, and it would reach its 

 maximum in a higher proportion of individuals. 



Variation in meat production. That the same principle is 

 operative in meat production is abundantly shown by experi- 

 ments. Steers were fed separately from calfhood to full maturity 

 at the Michigan Experiment Station. 1 The experiment was com- 

 menced as a breed test by Professor Samuel Johnson, and com- 

 pleted by the writer as a test of individual differences in ability 

 to put on gain in proportion to feed consumed. 



1 Bulletin A r o. 69, Agricultural Experiment Station, Michigan. 



