854 THE VAHIAHILITY OP COWs' MILK, i., 



definite relation between these quantities exists in the samples of 

 milk obtained from the different quarters of a cow's udder at one 

 milking. Their measurements of conductivity were made, how- 

 ever, upon milk from which the fat had been removed. These 

 relations are also shown by the diagrams representing the effect 

 of the number of calves or age of the cow, and the stage of 

 lactation or age of the calf, on the mean composition and pro- 

 perties of the milk (Text-figs. 5 and 6). 



Text-fig. 4 also indicates the existence of a direct relation 

 between the weights of milk obtained at a milking, and the 

 corresponding weights of fat. The mean weights of fat fluctuate 

 in the same direction as the mean weights of milk, and do not 

 show any tendency to remain constant and independent of the 

 amounts of milk. The present results are for single milkings, 

 however, and not for the daily outputs of the cows. The above 

 Figure shows also that there is a relation between the percentages 

 of lactose and the conductivity, and the weights of milk and of 

 fat. Cows producing larger quantities of milk thus show no 

 tendency to yield a secretion poorer in fat or in lactose than 

 those producing less milk under the same circumstances. 



Between the remaining mean values of the composition and 

 properties of the milk no distinct relations are shown by the 

 above diagram. The dependence of the density on the percent- 

 ages of fat and of ash, which is to be observed in certain in- 

 dividual samples, is not seen when the mean values are con- 

 sidered. There is also no evidence that a higher percentage of 

 fat is generally associated with a higher percentage of protein, 

 as was thought to be the case by Hart (1906), and by Eckels 

 and Shaw (1913). 



These results do not show the direct relation between the per- 

 centage of ash and the conductivity, which was observed by F. 

 Petersen (1904). 



Effect* of Breed. 

 In the following Table are given the mean composition and 

 properties of the milks of cows of different predominant strains 

 of breed. The numbers of cows of each strain vary from 51 to 



