292 Dr. Lyon Play fair on the Milk of the Cow. 



quantity of casein in the milk must either have diminished, or 

 the cow must have lost condition in giving this substance at 

 the expense of its tissues. 



The value of these experiments is certainly very much dimi- 

 nished by not being extended over a series of days on each 

 kind of food. But in England, where the price of aether is so 

 exorbitantly high, the expense of such experiments is a se- 

 rious consideration for a private individual. As they were 

 conducted under the same conditions with respect to tempe- 

 rature and exercise, an indication of the effects produced by 

 the various foods must have been obtained, although the final 

 effects have escaped detection. 



Neglecting the second day, in which an abnormal increase 

 of casein was produced by an accidental circumstance, we 

 find the milk of the third day contained 5*4 per cent, of casein, 

 that of the fourth 3*9 per cent., and of the fifth also 3*9 per 

 cent. The food consumed on the third day contained a very 

 large amount of casein, and this was immediately followed by 

 an increased amount in the milk. Some peculiar cause fa- 

 voured the flow of milk on the fifth day, in spite of the small 

 quantity of albumen in the food ; the milk derived its casein 

 from other sources. The milk of the second day contained 

 4*9 per cent, of casein, while that of the fourth day possessed 

 only 3*9 per cent, of the same constituent, although on that 

 day the cow had received 4 lbs. of albumen in its food, and on 

 the former day only one half or 2 lbs. 



Such are the changes which constantly occur to the dairy 

 farmer, and cause variations in the value of his milk, even 

 when the conditions of feeding seem to be the same. It is for 

 us to determine to what these seemingly discordant results are 

 due. 



In experiments such as these, we must remember that the 

 animal body is not a mere chemical laboratory, in which a 

 chemist may operate as he pleases. But there is a power, — 

 vitality, — superior to his, and it is only by its concurrence 

 that the changes which he desires are effected. 



Now, on the second day the animal struggled violently to 

 regain its liberty, and consequently expended much matter in 

 the production of force. It is difficult to conceive that any 

 waste of tissues can take place, without an alteration in their 

 chemical composition. Still we cannot deny (in the present 

 state of ourknowledge)]that an alteration in form might effect 

 a waste, as well as a change in composition. We know little 

 or nothing of the nature of secretion. All we know is, that 

 certain glands have the power of appropriating particular parts 

 of the organism or of food, and of producing fluids, which 



