Studies in Milk Secretion. 



Qi 



V 



•rH Q) 



Days 

 from 

 calv- 

 ing. 



Ave'ge 

 per 

 cent 

 fat. 



High'st 

 p-r 

 cent 

 fat. 



Time of 

 milking:. 



Time of 

 milking. 



Hours 



from 



previous 



niilking. 



Range 



of 

 varia- 

 tion. 



Tests Which Began More Than 6o Days from Calving. — Continued. 



165' 82 

 172 140 

 177J 6[ 



179 

 181 

 190 



206 

 210 



89 

 74 

 79 

 63 

 69 



65 



noon. 



night. 



noon. 



night 

 noon. 



night, 

 noon. 



6 a. m. 



Average. . 3.23 1.99 



Avg. all 

 old COW'S .3.17 1.76 



Avg. all I- 

 15 (lays. .. .3.20 1.62 



Avg. all 

 16-30 days. 3. 24 1.60 



Avg. all 

 31-60 days. 3.06 1.59 



Avg. all 

 61 — days. 3. 20 1.60 



Avg. of all 

 tests 3.16 1.60 



111 arranging the data given in Table III we had in mind four 

 questions : (i) Does the per cent of fat vary as the period of lacta- 

 tion advances. (By "period of lactation" is meant the time 

 intervening between two successive calvings.) (2) Is there a 

 variation in the per cent of fat between animals of different ages. 

 (3) At what time of day are the highest and lowest per cents of 

 fat found, and are they governed by the time of day or by the 

 length of time from the previous milking? (4) What is the 

 range of variation in per cent of fat found in different animals, 

 and is it more at one age than another ? 



In order to answer the first question, the records were grouped 

 according to age and according to the length of time from calving 

 to the beginning of the test. Four groups were made of each 

 age : I, of those cows whose tests began from one to fifteen da3^s 

 inclusive from the time they dropped their last calf ; II, of those 

 whose tests began from 16 to 30 days inclusive from that time; 



