856 THK VARIABILITY OF COWs' MILK,!., 



Among the physical properties, the greatest variation is shown 

 by the electrical conductivity, which ranges from 4*75 x 10~- 

 reciprocal ohms in the case of the Jersey strain, to 4*55 x 10~- 

 in the case of the Crossbreed strain. The variation of the mean 

 freezing point is within the limits of error of the determination. 

 The density varies from 1"0301 in the milk of Jersey and Short- 

 horn strains, to 1'0293 in that of Crossbred cows. 



The average numbers of calves of the cows of the different 

 strains range from 5 to 3. The average ages of the calves range 

 from 3*9 to 4*8 months. The data for the effect of the number 

 of calves or age of the cows, and of the period of lactation or age 

 of the calves, show that these variations are not large enough to 

 affect appreciably the present comparison of the mean values of 

 the composition and properties of the milk of cows of different 

 predominant strains. 



Efefct of number of calves or age of cow. 



Tn the following Table are given the mean values of the com- 

 position and properties of the milk of cows which have had 

 different numbers of calves, that is, of cows of different ages. 

 The number of cows at each age varies from 7 to 28. In this 

 case the means compared are those of rather widely varying 

 numbers of results, and are not so strictly comparable as they 

 would be, if the numbers of the cows at the different ages were 

 approximately equal. The numbers of calves of the cows ex- 

 amined range from 1 to 9; the ages of the animals, therefore, 

 range from 2 to 10 years. 



