208 OP THE BLOOD. 



One of the principal sources of their expenditure, however, is that combustive 

 process by which the heat of the body is maintained ; and the amount deposited 

 in the tissues as fat may be looked upon as the surplus of the quantity ingested 

 that is not thus consumed. The quantity of fatty matter in the blood is liable 

 to sudden augmentation, from the introduction of a large quantity furnished at 

 once by the alimentary material ; and this excess will continue until the surplus 

 has been eliminated, either by the combustive, the nutritive, or the excretory 

 operations. These last do not ordinarily remove the saponifiable fats from the 

 body ; for although the mammary secretion in the female draws off from her 

 blood a large quantity of fatty matter, this is destined not for its purification, 

 but for the nutrition of her offspring; and cholesterin appears to be the only 

 fatty substance which is normally excreted for the purpose of removing it from 

 the body. Fatty matters are often detectable in small quantities in the healthy 

 feces, where, however, their presence may be attributed to the non-absorption 

 of a portion of those which the food had included ; and this want of absorption 

 seems especially to occur in cases in which the action of the Pancreas is disturbed 

 by disease of that organ. 1 But they are sometimes discharged in such large 

 quantities that it is scarcely possible thus to account for their presence ; and it 

 would seem that they must have been poured into the alimentary canal either 

 by the liver or by some other excreting organ, which must have drawn them off 

 from the blood. It does not seem an improbable surmise that in such cases 

 there may be an extraordinary tendency to the metamorphosis of albuminous and 

 other azotized matters (whether furnished by the tissues or by the food) into fat 

 ( 40) ; and that the excretion of this substance does in effect tend to keep down 

 their proportion in the blood. Their occasional extraordinary accumulation in 

 the circulating fluid ( 176) tends to confirm this view ; for it appears scarcely 

 possible that such an enormous proportion of fat could have been derived from 

 the food, either in the condition of fat, or in that of a saccharine compound 

 capable of being converted into it. 



199. All the other Organic compounds which have been distinctly recognized 

 in the blood, or of whose presence in the circulating current we have inferential 

 evidence sugar, lactic acid, urea, uric acid, hippuric acid, creatine, creatinine, 

 the volatile fatty acids, and the odorous substances are to be considered not as 

 in any way subservient to those constructive changes in which Nutrition pro- 

 perly consists, but as products of the retrograde metamorphosis either of the 

 alimentary materials or of the tissues themselves, and as on their way to be 

 eliminated from the blood, either by the respiratory organs, or by some other 

 part of the excretory apparatus. And the more perfect the balance between the 

 action of this apparatus, 'and the operations whereby these compounds are gene- 

 rated, the less will be the proportion in which they present themselves in the 

 blood, and the greater will be the difficulty in detecting them there. 



200. The uses of the various Inorganic compounds, which, as being uniformly 

 present in the Blood, must be considered among its integral constituents, are not 

 as yet by any means positively known; yet great advances have been recently 

 made towards this knowledge; and it may be pretty certainly affirmed that the 

 presence of some of them has reference to the peculiar functions and conditions 

 of the blood itself, whilst others are chiefly destined for appropriation by the 

 tissues to whose growth it ministers. Thus the phosphate and carbonate of 

 soda would seem to have it for their chief purpose, to maintain the alkalinity of 

 the blood, on which its other properties so much depend ( 83), and to increase 

 the absorptive power of the serum for gases ( 84); the salts of potash, on the 

 other hand, appear to be specially required for the nutrition of muscular tissue 

 ( 85); whilst the presence of chloride of sodium is needed alike for the con- 



1 See Mr. A. Clark, in the " Lancet" for Aug. 16, 1851. 



