Wilson — Inheritance of Quantity and Qualitji in Coiosi' Milk. 473 



In the former ease, cows are calving at all times, while, in the latter 

 the majority calve early in spring and are dry during the dead of winter ; 

 and the records are kept in each case to meet the system of dairying : that is 

 throughout the year in the one and during the producing season in the other. 

 TJnder the whole-year system, there are cows whose full lactation periods do 

 not fall in any one year, while, under the cheese-making system, the records 

 of late-calving cows are kept for only a portion of their lactation period. At 

 tlie same time, under both systems, there are many cows too you.ng to have 

 attained what might be called their normal yield ; wliile, under the whole- 

 year system especially, records are kept of cows that have milked far beyond 

 the normal nine or ten months. 



To eliminate all such cases as far as possible, we make use only of tlie 

 records of cows aged four years and more that have been tested for not less 

 than thirty and not more than forty weeks. 



The cows whose records we can use may be separated into four divisions 

 of not very unequal numbers — viz., those yielding less than 500 gallons, tliose 

 from 500 to 600, those from 600 to 700, and those yielding over 700 gallons. 

 They could have been separated into more divisions than four \ but, on 

 consideration, this was found unnecessary. Among the lowest-yielding cows, 

 many give well below the 500, and, among the higher-yielding cows, a con- 

 siderable number give over 1000 gallons. But, in working through the 

 figui'es, it was seen that, if the very lowest- and the very highest-yielding 

 cows were given separate divisions to themselves, it would have made no 

 material difference to the general result. 



The results of this separation are expressed in diagrams 2, 3, 4, and 5. 

 These show that the quality of the milk given by any one of the four 

 divisions is almost the same as that given by the other three. Tlie curious 

 drop in the number of cows under the 500-gallon standard giving milk 

 containing 3'6 per cent, of fat may be taken as of no vital importance. 

 It is a phenomenon not strange in statistics. 



[Diagrams. 



