XV. 



MILK AND MILK PRODUCTS 



323 



Another important point in which the milks of cows of different 

 breeds differ, is in the average size of the fat globules. In any 

 one sample of milk the globules are very varied in size, but their 

 average dimensions can be estimated. At the New York Experiment 

 Station in 1891, a large number of measurements of the size of globules 

 of fat in the milk of cows of various breeds was made ; the results are 

 briefly summarised in the following table : 



AVERAGE DIAMETER OF MILK GLOBULES FROM COWS OF VAR.IOUS 

 BREEDS DURING WHOLE PERIOD OF LACTATION. 



In all cases, globules much larger (and also smaller) than the 

 dimensions given occur, but in the milk of Guernsey and Jersey cows 

 the larger globules constitute the greater portion of the total fat in the 

 milk, while in that of Ayrshire cows the large globules are very few 

 and constitute only a small proportion of the total fat present. 



These facts have an important influence on the readiness with 

 which the removal of cream can be effected, for it is obvious that large 

 globules possess greater buoyancy and therefore rise to the surface 

 much more rapidly than the small ones. In fact the very small ones 

 probably never separate at all. 



Morning's milk is said to have larger globules than evening's milk. 1 

 Change from dry winter food to green food in spring increases the size 

 of the globules. 2 



Influence of period of lactation. As a general rule it seems that 

 the proportion of solids in milk diminishes for a short time after calv- 

 ing, then begins to increase and continues to do so to the eighth or 

 ninth month after calving. The figures on the following page are from 

 the experiments at New York Experiment Station already alluded to 

 and give the average results obtained with 14 cows. 



The American observers also note a marked diminution in the 

 average size, but a great increase in the number of fat globules with 

 the advance of lactation. 



The author's experience agrees with the results of the American 

 investigation when stall-fed animals are considered. The results of 

 about 700 analyses of the milk of 17 cows made in the spring of 1900, 



1 Woll, Agric. Science, 1892, 441. 



3 Schnellenberger, Milch Zeitung, 1893, 817. 



