Studies in Milk Secretion. 93 



decided increase or decrease in the per cent of fat at any time up to 

 ninety days from calving. Beyond this time we can draw no 

 conclusions because less than one-tw^entieth of all the animals 

 were tested at a longer period from calving. 



We find that there is little variation in the average per cents 

 of fat between animals of different ages. Two-year olds average 

 3.12 per cent, three-j^ear olds 3.22, four-year olds 3.13, full aged 

 cows 3.17, and the average of all ages 3.16. 



In order to answer question (3) as to the time of day at which 

 the highest and lowest per cent of fat was found in the milk, we 

 arranged in Table III along side of the highest and lowest per 

 cent of fat found during the seven days, the number of hours 

 which had elapsed between the milking at which such per cent 

 was found and the milking just preceding. These figures may 

 be seen in Table III in the columns marked "Hours from prev- 

 ious milking. ' ' Collecting together all those instances where the 

 per cents were highest at morning, noon, and night, wnth the 

 hours intervening between milkings, we have the following 

 averages : 



No. of instances at which Average number of 

 Time of milking. the milk was highest hours from previous 



in fat. milking. 



Morning 8 8.37 



Noon 117 7-44 



Night 74 6.59 



Total and average 199 7- 16 



Collecting the instances of the lowest per cents of fat in the 

 same manner, we have the following averages : 



No. of instances at which Average number of hours 



Time of milking. the milk was lowest in fat. from previous milking. 



Morning 165 9-47 



Noon 12 7-79 



Night . 25 7-72 



Total and average 202 9. 16 



In the morning the average number of hours preceding the 

 lowest per cents of fat exceeds the number of hours preceding 

 the highest per cents of fat by i.i hours. In like manner at 

 noon the excess of hours following lowest per cents of fat over 

 those following highest per cents of fat is .35, and at night the 



