Butter-Fat Percentage in Jersey Cattle. 141 



the similar variation of the lipin portion of the milk the lipin 

 portion of the egg calls attention to the lack of knowledge con- 

 cerning the exact nature of this secretory activity of the mam- 

 mary gland and the possibility that there may be two types of 

 cells in this gland of separate and distinct function. 



Returning to Table I, no skewness is present in three of the 

 nine distributions. In the remaining six distributions at the 

 different ages there are four in which the skewness is plus and 

 two in which the skewness is minus. The frequency distribu- 

 tions of butter-fat percentage at the first three years of the lac- 

 tation life of the Jersey cow are skew in the plus direction. This 

 skewness increases to the fifth year of lactation. At this age 

 the curves for the butter-fat percentages are symmetrical. The 

 minus skewness of the eight and nine years of age are quite 

 unlooked for. Negative skewness is on the whole, rare. Why 

 milk production at these ages should change to become minus 

 and minus to as large an amount in the ninth year of age is not 

 clear. 



The general frequency distribution for the butter-fat per- 

 centage of Jersey milk has a plus skewness of rather small 

 amount. The comparison of the skewness for this Jersey data 

 with that of other breeds is given in Table 2. These data show 

 that butter-fat percentage of the four breeds, Jersey, Holstein- 

 Friesian, Ayrshire and Guernsey is plus and of small amount. 

 The distribution of each breed have approximately the same 

 numerical value for this constant. 



Comparison of the skewness of the other milk solids with 

 those of the butter-fat percentage distributions show these dis- 

 tributions are, within the limits of random sampling equal in 

 their asymmetry. 



The comparison of the skewness of the percentage com- 

 position of the parts of the egg reveals the fact that the skew- 

 ness of the percentage of shell is of about equal amount with 

 those of the different parts of the milk. The skewness of the 

 percentages of yolk and of albumen are slightly greater than 

 those of any of the butter-fat percentages contained in the milk 

 of the different breeds. In comparison with their probable er- 

 rors the difference between these values is in certain cases un- 

 doubtedly significant in other cases the significance of the data 

 is not so clear. 



