8 MODERN METHODS OF TESTING MILK 



conditions of surroundings during the day and night, 

 there appears to be a common tendency for the pres- 

 ence of a little more fat in the morning's milk, even 

 when milkings are apart the same length of time. 



(6) Variation of fat content in different portions of 

 milk drawn from the udder. The following figures, 

 taken from the writer's records, illustrate the general 

 rule that the first milk drawn contains least fat, the 

 milk last drawn (stoppings) being the richest in fat: 



Per cent, of fat in milk 

 cow i cow 2 cow 3 



First portion drawn .... 0.90 1.60 1.60 

 Second portion drawn . . . 2.60 3.20 3.25 

 Third portion drawn .... 5.35 4-io 5oo 

 Fourth portion drawn (strip'gs) 9.80 8.10 8.30 



It is also known that the per cent, of fat in milk 

 varies in different quarters of the udder of a cow, and 

 also varies more or less in each quarter with the order 

 in which the teats are milked. 



THE NITROGEN COMPOUNDS OF MILK 



Some confusion prevails in respect to the names of 

 the nitrogen compounds of milk. They have been 

 spoken of as albuminoids, proteins, etc. Frequently 

 the word casein is erroneously used to include all the 

 nitrogen compounds of milk. 



How many nitrogen or protein compounds are pres- 

 ent in normal milk ? What are they ? Different work- 

 ers have reported from one to seven or more. The 

 chemical evidence at hand justifies us in the belief that 

 normal milk contains, in appreciable amounts, not 

 more than three nitrogen-containing or protein bodies, 



