42 THE NORMAL COMPOSITION OF MILK 



in the quality of milk, the fat content of Monday's milk being 

 usually slightly lower than that of the other days, but this is 

 apparently due to the usual intervals between milkings being 

 slightly disturbed during the week-end. 



The intervals elapsing between milkings have been shown by 

 various observers to have an influence on the percentage of 

 fat, though relatively little on the absolute amount. Fleisch- 

 mann 6 found morning milk slightly richer than evening milk 

 and decided that the fat content varied with the intervals 

 between milking. Richmond 7 as the result of over 100,000 

 analyses made during sixteen years, gives the figures for the 

 fat content of morning and evening milk as 3.56 and 3.93 per 

 cent, respectively; the intervals being 10.8 and 13.2 hours. 

 His results also show that the difference is more marked during 

 the summer months. Eckles and Shaw 8 found that with equal 

 intervals between milkings, the morning milk was slightly higher 

 in fat content than the evening milk. The Reichert-Meissl 

 and Koettstoffer numbers of the butter fat were usually lower, 

 and the iodine number usually higher in the evening milk, while 

 no appreciable constant variation could be detected in the 

 physical characteristics. With animals milked more than 

 twice daily, the variations in the fat content of the milk were 

 larger and the highest value was usually found in the milk 

 drawn near the middle of the day. The explanation of this is 

 probably connected with the interval between feeding and 

 milking. 



The influence of the stage of lactation upon the fat content 

 of milk has been the subject of much experimental work, and 

 although some of the data is slightly contradictory, it has been 

 generally established that the percentage of fat usually de- 

 creases during the first three months of lactation, then remains 

 fairly constant for four to five months, and, finally, rises rapidly 

 to a maximum. This process is well illustrated by the results 

 of Eckles and Shaw 9 which are given in Table XVII. 



The chemical and physical characteristics of the butter fat 

 obtained in these experiments are recorded in Table XVIII. 



