VARIATIONS IN COMPOSITION. 319 



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

 dimensions given occur, but in Guernsey and Jersey cows the 

 larger globules constitute the greater portion of the total fat in 

 the milk, while in 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. :;c Change from dry winter food to green food in spring 

 increases the size of the globules. 1 



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

 that the proportion of solids in milk diminishes for a short 

 time after calving, then begins to increase and continues to do 

 so to the eighth or ninth month after calving. The following 

 figures are from the experiments at New York Experiment 

 Station already alluded to and give the average results 

 obtained with 14 cows : 



Composition of milk during each month of lactation. 

 Period of lactation. Fat. Casein. Sugar. Ash. Total solids. 



First month ... 4-86 3*53 5-00 0'69 14-09 



Second ,, 



Third ,, 



Fourth 



Fifth 



Sixth 



Seventh ,, 



Eighth ,, 



Ninth 



Tenth ... 4-46 3-81 5-39 0'73 14-41 



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. 



* Woll, Agric. Science 1892, 441. t Schnellenberger, Milch Zeitung 1893, 817. 



