[ 546 



XL. 



AN ECONOMIC METHOD OF DETERMINING THE AVERAGE 

 PERCENTAGE OF FAT IN A COW'S MILK FOR A LACTATION 

 PERIOD. 



By E. J. SHEEHY, F.R.C.Sc.L, 



Demonstrator in Zoology, Royal College of Science, Dublin. 



[COMMDNICATICD HY PROFESSOR JAMICS WILSON, M.A., U.SC.] 



(Plates LIL, LIII.) 



Itead NovuMiiER 19, 1918. Published May 13, 1919. 



The irregularity of the returns for fat percentage in cows' milk often obtained 

 by the usual method of testing a number of samples taken at intervals during 

 a lactation period has occasioned comment. Similarly, in experiments on the 

 comparison of the fat-producing value of foods, observers have sometimes 

 doubted the accuracy of the actual results because of some unaccountable 

 diversion from the expected. This occurs when the average milk fat per- 

 centage is determined from samples taken at intervals during the period of 

 investigation. Experiments of this nature are often conducted without a 

 full appreciation of the difficulty of ascertaining accurately what might be called 

 the mean fat percentage. The difficulty in this connexion arises from the 

 fact that all cows exhibit some, and many cows exhibit very great, variation 

 in the daily returns. To investigate this phenomenon an experiment was 

 conducted in 19 15 at the Albert Agricultural College on eleven cows during 

 the period June 23rd to August 1st (inclusive), i.e., during a period when the 

 cows were under continuous normal conditions in the field. 



