xii AUTHOR'S PREFACE. 



to a continuous metamorphosis, which may be regarded as the 

 expression of its vitality. The nutrition of the peripheral sys- 

 tem is effected by the liquor sanguinis, not by the blood-cor- 

 puscles. The liquor sanguinis affords nutriment to the cells 

 and organs, which possess an inherent power of selecting proper 

 material, or of forming it from non-homologous matter, at the 

 same time secreting the products of decomposition. The prin- 

 cipal nutritive matters in the liquor sanguinis are albumen, 

 fibrin, and fat. The chief products of this metamorphosis are 

 the extractive matters and lactic acid, which occur in the ex- 

 cretions, especially in the urine. Urea, bilin, and carbonic acid 

 are either not products of the metamorphosis of the blood during 

 the act of nutrition in the peripheral system, or at most they 

 are only in part formed by it. They must be regarded as pro- 

 ducts of the vital energy of the blood-corpuscles, which, doubt- 

 less, possess the same power of attracting nutriment, and of 

 throwing off decomposed products, as other living cells. The 

 proper nutriment of these corpuscles is oxygen, albumen, and 

 probably also fat, which are furnished them by the liquor san- 

 guinis. The most important products of their metamorphosis 

 are carbonic acid, urea, fibrin, extractive matters, and very pro- 

 bably some of the constituents of the bile. The leading and 

 most important object of this \dtal energy of the blood-corpus- 

 cles is the production of animal heat, without which every 

 function of the organism, nay even life itself, would be instan- 

 taneously annihilated. The production of animal heat is due 

 to the combination of oxygen with the carbon of the globulin ;i 

 the principal products of this reaction are carbonic acid and 

 urea, or uric acid, (which is excreted as a substitute for urea in 

 most of those classes of animals in which elliptic blood-corpus- 



' [Simon's views respecting the production of animal heat approximate closely 

 to those expressed by our countryman, Mr. Anccll, in his lltli lecture on the 

 blood. See Lancet, 1840, vol. i. p. 829, or Dr. Posner's German edition of the col- 

 lected lectures, p. 200.] 



