Abstracts. 291 



different lactations as they effect milk production make them- 

 selves felt in the correlation coefficients ; in the second case the 

 use of the total milk production gives a mean of these environ- 

 mental effects. The outcome of this study shows the environ- 

 mental changes reduce the correlation one-seventh to one-eighth 

 of what it would be under the conditions of an average environ- 

 ment. This result makes it clear that for these Jerseys heredity 

 plays a greater part in their milk production from lactation to 

 lactation than environment. < 



The correlation coefficients for the milk production of one 

 lactation with that over several lactations, furnishing as it does 

 the basis for the regression formula by which milk production 

 over long periods may be predicted from shorter ones, is of the 

 greatest practical importance in culling the herd of the mediocre 

 animals. The use of these coefficients is illustrated by table. 



The relative contribution of the different lactation to the 

 total milk production over a longer period shows that the fac- 

 tors which govern milk production have their regulatory power 

 maintained in the same relative strength throughout the life 

 of the cow to the exclusion of any group of factors acting with- 

 in this life for any short period. 



STUDIES IN MILK SECRETION. VI. ON THE VARIA- 

 TIONS AND CORRELATIONS OF BUTTER-FAT 

 PERCENTAGE WITH AGE IN JERSEY 

 CATTLE.* 



This paper has as its object the presentation of quantita- 

 tive data along with the biometrical analysis of the same, on the 

 normal variations and correlations of the butter-fat percentage 

 contained in Jersey milk during the different lactations of the 

 cow's life. In this sense this paper is the copartner to the pre- 

 vious paper in this series dealing with the variations of milk 

 yield for these same Jersey cow t s. The data used for this study 

 are especially suited to the objects of this investigation. They 

 are from a strictly homogeneous group of records for the butter- 

 fat percentage of normal, healthy, pure bred Jersey cows main- 



*This is an abstract from a paper by John W. Gowen having the 

 same title and published in Genetics, Vol. 5, No. 3. 



