Jan. 20. 1919 Variations and Mode of Secretion of Milk Solids 99 



These conclusions give us two variables which influence the concentration 

 of butter fat and solids-not-fat differently. This difference in action of 

 these variates proves that the butter fat and the solids-not-fat can not 

 have a common mother chemical from which they are derived from split- 

 ting. 



(4) Correlations are presented between the variables, pounds of milk, 

 butter fat, and solids-not-fat. Each variable is highly correlated, the 

 correlation ranging from r = 0.8644 ±0.0093 to /- = 0.9497 ±0.0036. In 

 each case the regressions are linear. The partial correlation between 

 butter fat and solids-not-fat for a constant value of the milk is found 

 to be 0.5635 ±0.0252. This correlation, together with those above, fur- 

 nishes the data necessary to establish the conclusion that some of the 

 factors responsible for high concentration of butter fat are also respon- 

 sible for high concentration of some of the solids-not-fat in cow's milk. 

 Another important practical conclusion may be drawn from this correla- 

 tion ; that if it is desired to improve either the butter fat or solids-not-fat 

 concentration in a given herd the determination of the concentration of 

 either solid will also result in an increased concentration of the other 

 solid. 



(5) Data on the diurnal variation of cow's milk are presented. These 

 data show that the morning milk is between 0.678 and 0.723 per cent 

 lower in butter fat than in the evening milk throughout the whole lac- 

 tation. No appreciable difference occurs in the solids-not-fat. These 

 data offer criteria between the theories to account for the secretion of the 

 milk solids. In the cell-disintegration theories the cell must contain a 

 fixed quantity of solids-not-fat, while the butter fat varies so that in the 

 longer interval between milkings the cell accumulates less fat than in the 

 short time; or, taken the other way, the cell contains relatively more 

 protein and sugars than fat as the interval between milkings lengthens. 

 This is contrary to our knowledge of fat formation, for it is commonly 

 accepted that first comes the cells composed largely of protoplasm and 

 that as time goes on this cell is more and more loaded with fat at the ex- 

 pense of the protoplasm. Unless these mammary cells behave very differ- 

 ently in the formation of this fat than other body cells, this variation is 

 enough to discredit seriously the hypothesis of cell disintegration to ac- 

 count for these milk solids; and in fact, to make it an absurdity. Fur- 

 thermore, so far as our knowledge of the variations of secretory glands 

 goes, the variations of the milk fall in well with the secretory hypothesis 

 to account for these solids. 



LITERATURE CITED 

 (i) AsHCROFT, William. 



1905. THE MILKING TRIALS OF 1904. In Jout. Bfit. Dairy Farmers' Assoc. 

 V. 19, p. 88-117. 



