20 MILK [in 



put it in another way, the number of globules of 

 different sizes is in inverse ratio to their size. It is 

 also to be noted that the size of the fatty globules in 

 the milk of the same cow is not at all times, and 

 under all conditions, the same ; and probably even a 

 greater difference exists in those of the milk of cows 

 of different breeds. 



Some conception of how numerous these minute 

 fat globules are in milk may be inferred from the 

 statement that it has been calculated that their 

 number in a kilogram of milk (about 2J Ibs. or If 

 pints), containing 4 per cent of fat, amounts to from 

 eighty thousand millions to twenty billions, according 

 as we take the globule to be of the largest or of the 

 smallest size; or, to put it in another way, their 

 surface area would amount to from 25 square metres 

 (about 30 square yards) to 157 square metres (about 

 188 square yards). 



While the opacity of milk is chiefly due to the 

 fatty globules, it is also due to the fact that a portion 

 of the mineral and nitrogenous matter is present in 

 a state of suspension. Milk in thin layers, however, 

 is not absolutely opaque, and it has been proposed 

 to test the percentage of its fat by taking advantage 

 of this fact and estimating its degree of opacity. A 

 thin layer of milk is examined, and the amount of 

 light it retards is noted. But this so-called " optical 

 method" of estimating fat is very unreliable, since 



