316 GENERAL REVIEW OF NUTRITIVE OPERATIONS. 
milk of the Human female; and that of sugar in the milk of 
the Mare. The milk of the Cow, if a portion of its casein 
were removed, would resemble Human milk more nearly than 
any other; and it is therefore best for the nourishment of 
Infants, when the latter cannot he obtained. The important 
influence of Mental emotion on this secretion has already been 
noticed (§ 353); and many more instances might he related, 
were not the ordinary facts in regard to it generally known. 
CHAPTER VIII. 
GENERAL REVIEW OP THE NUTRITIVE OPERATIONS—FORMATION 
OF THE TISSUES. 
General Review of the Nutritive Operations. 
378. In the preceding Chapters (hi. to v.) those processes 
have been described, by which the alimentary materials that 
constitute the raw material of the tissues, are converted into 
a fluid adapted for the Nutrition of the body; and we then 
(Chaps, vi. and vii.) considered those functions, by which this 
fluid is kept free from the impurities it acquires during its 
circulation through the body, and is maintained in the state 
which alone can adapt it to the purposes it is destined to fulfil. 
These purposes may be regarded as fourfold. In the first 
place, the Blood is destined to supply the materials of the 
fabric of the body; which, as it is continually undergoing 
decay (§ 68), requires the means of as constant a renovation. 
Secondly , the Blood (in most animals at least) serves to convey 
to the tissues the supply of oxygen which is required by 
them,—especially by the muscular and nervous tissues,—as a 
necessary stimulus to the performance of their functions. 
Thirdly , the Blood furnishes to the secreting organs the 
materials for the elaboration of the various fluids, which have 
special purposes to serve in the Animal economy,—such, for 
instance, as the Saliva, Gastric juice, Milk, &c. And lastly , 
the Blood takes up, in the course of its circulation, the pro¬ 
ducts of the waste or decomposition of the various tissues, 
which it conveys to the several organs,—the Lungs, Liver, 
