824 THE VARIABILITY OF COWS' MILK, i., 



The results obtained have been submitted to a simple statistical 

 treatment, by which the most probable values of the ciuantities 

 measured, and their relative variabilities, have been determined. It 

 has been found that the quantities measured fall into three sharply 

 defined groups, as regards their variability: the values of certain 

 physical properties are least variable, the concentrations of the 

 substances present are more variable, and the amounts of these 

 substances obtained at a milking are most variable. The concen- 

 trations of the substances in solution are considerably less variable 

 than those of the substances in suspension. 



Methods. 



The cows examine d — The cows, from which the samples 

 of milk described were obtained, were all kept in the dairies 

 attached to certain Government Mental Hospitals in the vicinity 

 of Sydney. The whole output of the cows was consumed in the 

 Institutions to which they were attached. The following data with 

 regard to the cows were obtained from the dairy stock-books. 



(1) The breed of the cow. In nearly all instances, the cows 

 were crossbred, and the breed given is that of the predominating 

 strain. 



(2) The number of calves, to which the cow liad given birth at 

 the time of the collection of the samples of milk. In the cases of 

 cows Nos. 23-46, records of the numbers of calves could not be 

 obtamed. Records of the ages of the cows Avere available, how- 

 ever; and to make the data for these cows uniform with those for 

 the others, the numbers of calves have been calculated from the 

 ages, on the assumption that the first calf was born when the cow 

 was two years old, and that, after that age, one calf was born every 

 year. The numbers of calves calculated in this way are only 

 approximate. 



(3) The period which had elapsed between the birth of the last 

 calf, and the collection of the sample of milk. This period is 

 exjjressed in Table ii. below, in days. 



