'238 
The Applications of Physiology 
cannot ajjain be separated from the body without being in union 
either with carbon or hydrogen, it is indispensable that both of 
these elements should exist largely in the food of the young ani- 
mal. But it is quite as indispensable that the food should contain 
materials fitted for the increase of its growing frame. Both these 
conditions are united in the milk of the mother. I subjoin the 
composition of the milk of several animals : — 
Woman.* 
Cow.t 
Ass.| 
Playfair. 
Play fair. 
'"PHigotT 
Casein . . 
. 1-51 
4-0 
1-95 
Butter . . 
. 4-37 
4-6 
1-29 
Sugar of milk 
. 5-75 
3-8 
6-29 
Ashes . 
, 0-53 
0-6 
Solid matter 
. 12-19 
13-0 
9-53 
Water . . 
. 87-81 
87-0 
90-47 
100-00 
100-0 
100-0 
Casein is precisely the same in composition as animal flesh, 
and hence supplies matter adapted for the growth of the body. 
Butter and sugar are destined for the support of respiration, and 
consequent maintenance of animal heat. Butter is a substance 
admirably suited for this purpose ; for, being of a combustible 
nature, it yields much heat by its union with oxygen. Sugar also 
is well adapted for the support of respiration, from causes which 
I explained in my former lectures. The milk of the ass is very 
similar in composition to that of woman ; both are remarkable 
from their large proportion of sugar. The milk of the cow con- 
tains more casein and butter, and less sugar, than that of either of 
the previous animals. The ashes of milk consist principally of 
common salt and the earth of bones. It also contains potash and 
oxide of iron. The soda of the common salt is necessary for the 
formation of bile, as I stated in my last lecture, whilst its muriatic 
acid aids in the process of digestion. 
In milk, therefore, we find united all the conditions for the life 
of a young animal. Its rapid respiration, and the high tempe- 
rature of its body, are supported by the butter and sugar of the 
milk. The casein furnishes matter for its growth, and the ashes 
the materials for the formation of the bones, and necessary con- 
stituents of the blood. 
* Tlie milk was taken from a farmer s wife, a strong healthy female, of 
twenty -eight years of age. The specimen analysed was obtained on the 
twenty-iirst day after her confinement, the child being her third ; her food 
consisted principally of gruel. She was confined to bed; and on this 
account the casein may be in smaller quantity than usual, and the butter 
in excess. 
t The analysis of the milk of the cow is the average of several analyses 
of milk taken when the cow was in the field. 
% Peligot, An. de Ch. et de Phys., vol. Ixii., p. 432. 
