to the Rearing and Feeding of Cattle 
247 
understood. We know, for example, that the albumen contained 
in the serum of blood may be converted into casein by mixture 
with a little caustic potash (Scherer) : but we are entirely ignorant 
how the conversion is effected in the animal economy. Potash is 
quite indispensable to the formation of milk, and hence it is 
highly probable that the transformation of albumen into casein 
proceeds in the way already described : but it does so under the 
direction of vitality; for we are aware that the composition of the 
secretion of milk or tears is influenced by nervous and mental 
affections, as well as by many other causes which tend to alter the 
state of the vital forces in the body. 
It is a question of some interest, whether the amount of casein 
in milk is increased by the waste of the tissues of the body ? The 
milk of a cow in the meadow contains more casein than that of a 
stall-fed cow ; and I have found that the evening's milk generally 
contains more casein than milk obtained in the morning. In the 
first case, the cow in a meadow obtains exercise, and consequently 
the tissues of its body undergo a certain degree of waste ; while in 
the latter case a similar condition holds, for during the day a cow 
has more exercise than at night : still these cases might be ex- 
plained on the supposition that the proportion of butter, sugar- 
of-milk, and water, in the milk, varied in the different states. 
But another strong proof of our view is drawn from the composi- 
tion of the milk \){ a cow immediately after its parturition. 
During labour the muscles are thrown into a violent state of 
action, which occasions a proportionate waste of the tissues of the 
body : as parturition generally continues for several hours, the 
waste of matter in the body is very considerable. Now if this 
waste of the tissues actually increased the amount of casein in the 
milk, we should expect to find a notable increase of that body in 
the milk of a cow which has just calved : and this we know to be 
the case ; for such milk is quite thick with cheese. Boussingault 
found the composition of the milk of a cow, before the calf had 
been allowed to suck, as follows : — 
Casein . . 15.0 
Butter . . 2.G 
Sugar . . 3.6 
Ashes . . 0.3 
Water . . 18.5 
100.0 
Here then we find that the milk contained 15 per cent, of 
casein, while the milk of the same cow usually contained only 
3 per cent., or one-fifth the quantity. I am quite aware that 
there is some difficulty in conceiving a separation of part of the 
organism without a destruction of its chemical composition ; but, 
