862 THE VARIABILITY OF COWs' MILK, i., 



and during- the remainder of the period rises again, finally reach- 

 ing its initial value. 



Tlie percentage of lactose falls steadily during the whole period 

 of lactation, the final value being about 10% lower than the initial 

 value. 



The variation of the percentage of total solids is dependent on 

 that of the separate constituents. This value, like that of the per- 

 centage of protein and of ash, falls at first, and then rises again. 



The value of the conductivity increases steadily during the 

 whole period of lactation ; the final value being about 10% 

 higher than the initial. 



The values of the density and of the freezing'-point remain con- 

 stant through the whole course of lactation. 



The weight of milk obtained at a milking falls steadily and 

 rapidly as lactation proceeds, the yield towards the end being less 

 than half of what it was at the beginning. 



The weight of fat obtained at a milking also tends to fall 

 steadily during the whole period of lactation, and to about the 

 same extent as the weight of milk, in spite of the fact that the per- 

 centage of fat tends to increase. 



As was stated above, the weights of the remaining constituent? 

 are more dependent on the total amount of the milk than is the 

 weight of fat. The weights of these constituents will, therefore, 

 fall steadily during lactation with the weight of the milk. 



In conclusion, I wish to express my indebtedness to Professor 

 Sir Thomas Anderson Stuart, in whose laboratory this work was- 

 done; and to Dr. E. Sinclair, Inspector General of the Insane, by 

 whose courtesy the samples of milk discussed in this paper were 

 obtained. I also wish to thank Dr. H. G. Chapman for his helpful 

 criticism during the progress of the work. 



Summary. 



The variations of the composition and properties of samples 

 of afternoon-milk from 109 normal cows are discussed. 



The following were the most probable values of the quantities 

 measured: depression of freezing-point, 0*562°C.; density, 1-0297; 



