SOURCE OP THE BUTTER OF MILK. 229 



of its salts, are acknowledged on all hands to pre-exist in the The galtg of 

 blood ; and these, constituting about -^ of its solid ingredi- milk exist in 

 ents, must be admitted to pass into the secretion by strainage 

 only. Of the other solid ingredients, the fat, which constitutes about one 

 fourth, also exists in the blood, being derived by lacteal absorption from 

 the food. 



Do milk-giving animals, then, find in their ordinary dief a sufficient 

 quantity of oleaginous material to supply the drain establish- The hydrocar . 

 ed through the mammary gland, and the calorifacient de- bons pre-exist 

 mand, supposing none to be made in the system ? The re- 

 searches of Dumas have definitely settled this question. Of these the 

 following is an abridgment : 



Fat in Articles of Forage. 



Indian corn 8.75 per cent. 



Kice 1.00 



Oats 3.30 



Eye 1.75 



Wheat 2.10 



Dry hay 2.00 



Clover in flower 4.00 



Wheat straw 3.20 



Oat straw 5.10 



Beet root 0.05 



Potatoes 0.08 " " 



A cow in good condition, eating 100 pounds of dry hay, will furnish 21 

 quarts of milk, from which there can be obtained 1J pounds Quantity of fat 

 of butter. If this butter was obtained exclusively from the in fora s e - 

 food, and none made in the system, we ought to find in the 100 pounds 

 of dry hay 1J pounds of fatty matter; but sulphuric ether can remove 

 from such hay 2 pounds, and in several specimens of clover cut in flow- 

 er, M. Boussingault found the proportion as high as 4 per cent. We 

 may therefore affirm, relying on the universal experience of farmers, that 

 the hay eaten by a milch cow contains more fat matter than the milk 

 which she yields. Thus far, therefore, we are not authorized to regard 

 the animal as capable of producing the butter found in its milk, but, on 

 the contrary, we may be led to suppose that the whole of it is taken 

 from the food. 



In a physiological point of view, a single experiment of this kind is 

 insufficient. Errors may arise in comparing together hay taken by 

 chance, and the produce of milk taken by chance. It would doubtless 

 be far better to establish a direct experiment, giving the proportion of 

 butter, determined by analysis, relatively to the proportion of fat matter 

 consumed by a cow. This experiment has been made on such a scale 

 and with so much care as to be very convincing. It lasted for a year, 

 and was conducted on 7 milch cows, the milk, drawn twice a day, being 



