98 A MANUAL OF MENDELISM 



in which they had been hatched so soon as their per- 

 formances showed them to belong to the other. Yet, 

 after ten years, the pullets produced in the section with 

 good hens were no better than those produced in that 

 with bad. The proportions of good and bad layers 

 produced in each were about the same. No simpler 

 experiment could be devised, for the two sections differ 

 in one point only : the one in containing good hens 

 while the other contains bad : yet the result is the 

 same in both. Clearly, therefore, improvement is not 

 to be achieved through the hens. 



In 1908, the work was placed in Dr. Pearl's hands, 

 and his solution of the problem, together with all the 

 essential data, can be found in Bulletins 166, 192, and 

 205 of the Maine Agricultural Experiment Station. 



Problems of production the result of vital activity 

 are surrounded with difficulties, not the least of which 

 is the collection and orderly arrangement of the large 

 amount of necessary data. Animals are very liable to 

 vary in food-supply, comfort, and health and, accord- 

 ingly, in productive activity, and much information has 

 to be collected in order to determine the normal rates of 

 production before any inferences can be drawn and 

 to identify abnormal results and treat them with fair- 

 ness and good judgment. Besides, animals, as a rule, 

 must have covered a considerable portion of their 

 normal lifetime before their rate of production is re- 

 vealed, and, in the meantime, many disturbing factors 

 may have intervened. 



Happily Dr. Pearl was able to discover a method of 

 determining a hen's laying capacity shortly after she 

 had begun to lay, and, by this, to decrease not only 

 the necessary statistical labour but also the chances 



