4-58 On the Law of the Nutrition of A^iimals. 



Another table gives the average quantity of solid consti- 

 tuents of the milk for periods of five days. 



The milk consists of— water, 87-19; butter, 3-70; sugar, 

 4-35; caseine, 4--16; sol. salts, 0'15 ; insol. salts, 0-44. The 

 constituents of the butter are oil,86'3; caseine, 0*9; water, 12'8. 



The fact that not merely the quantity of milk but also that 

 of the butter increases with the amount of nitrogenous matter 

 in the food (that is, with the proportion of plastic nourishment), 

 is worthy of notice; for from the absence of nitrogen in the 

 butter, vve should be apt to expect the contrary. Playfair, in 

 his experiments, has certainly inferred this ; for according to 

 him, those substances which do not contain nitrogen (potatoes, 

 &c.), yield milk rich in butter, and rest (stall-feeding) acts in 

 the same way ; while if the animal be allowed to feed on poor 

 pasture, where it must move about a good deal, it yields milk 

 rich in caseine. But his experiments are continued for such 

 short periods, that important conclusions cannot be deduced 

 from them. From Dr. Thomson's observations, we find that 

 if a cow always receives the same kind of food, the quantity 

 of milk gradually decreases ; but if its diet be changed, it 

 rapidly increases. A frequent change of diet is therefore 

 advantageous. He has also established the rule, that the 

 quantity of milk obtained from a cow is greater in the morning 

 than in the evening. 



When fed on barley and hay, they yielded — 



[The following observations of Dr. Knapp are founded on a 

 table given by Dr. Thomson, deduced from his own experi- 

 ments, in which the relation between the nutritive and calori- 

 fiant matter is stated for different kinds of food. * 



• This number is 25-69 in the original German, but has been recalculated 

 from the English data. — Tb. 



