206 THE CREAMERY PATRON'S HANDBOOK. 



contained a residue of rich milk and it is probable that the whole of the fat 

 is never drawn at each milking. 



There has been a large number of theories advanced as to the methods 

 by which milk is elaborated, most of them based upon the assumption 

 that it is a comparatively simple chemical and physical problem. All the 

 earlier theories were based upon such assumption, the physiologist regarding 

 the mammary gland as an organ to separate certain elements from the blood 

 in definite proportions as milk. It was regarded that the process was largely 

 *one of transudation through a special membrane, on the same principle 

 that exchange of gases by osmosis, occurs rapidly in the tissues of the lungs. It 

 was assumed that the fat of the food, and the water and the salts taken 

 into the alimentary canal were absorbed and taken into the blood and then 

 eliminated by the mammary gland. The milk serum was regarded as 

 escaped blood serum, and that the other products were derived from the 

 blood or epithelial cells. The gland was assumed to be a semi-passive organ, 

 receiving the milk already prepared, and only requiring elimination 

 in the proper proportions. 



It was upon the foregoing assumption, that the great majority of 

 experiments have been made for the purpose of augmenting the quantity 

 or quality of the milk. If this assumption were correct, then the quantity 

 or quality of milk produced would only be limited by the ability to digest 

 and assimilate food. 



Probably the most satisfactorily planned and executed experiment 

 to settle this theory was made by Jordan and Jenter. 1 The object 

 was to determine whether the fat in the milk was derived from the fat in 

 the food. During the entire experiment of fifty-nine days, analyses were 

 taken of the feeds and milk and the urine and faeces collected to determine 

 where everything had gone. For two weeks the cow (a grade Jersey) was 

 fed on ten pounds of timothy hay, six pounds of corn meal, five pounds 

 of ground oats and one pound of wheat gluten. Then the same foods 

 were fed with all or very nearly all the fat extracted. For a short time after 

 the change there was a decided variation in the milk solids, but this was 

 soon overcome, and the milk regained its normal composition and main- 

 tained it with only slight variations, that could not be assigned to any cause, 

 throughout the entire period. The milk fat yield for the seventy-five days 

 was 62.9 pounds and the food fat contained 11.6 pounds, of which only 

 5.7 pounds were digested. This extra fat could not have come from the 

 previously stored body fat, because in the beginning of the experiment 

 the cow was thin in flesh and gained forty-seven pounds of body weight, 

 and was judged to be a fatter cow at the end than at the beginning. The 

 milk fat could not have come from the protein, because during the fifty- 

 nine consecutive days, 38.8 pounds of milk fat was secreted and the urine 

 nitrogen was equal to about 33 pounds of protein. According to any 



1 Bulletin 132 New York State Experiment Station. 



