[CHAPTER XIV.]
OF NUTRITION.
Composition of the blood—Liquor sanguinis—Recent account of the structure of the red particles—Formation of the red particles in the incubated egg—Primary motion of the blood—Vivifying influence of the red particles—Influence of arterial and venous blood on animal and organic life—Formation of human blood—Course of the new constituents of the blood to the lungs—Space of time required for the complete conversion of chyle into blood after its first transmission through the lungs—Distribution of blood to the capillaries when duly concentrated and purified—Changes wrought upon the blood while it is traversing the capillaries—Evidence of an interchange of particles between the blood and the tissues—Phenomena attending the interchange—Nutrition, what, and how distinguished from digestion—How the constituents of the blood escape from the circulation—Designation of the general power to which vital phenomena are referrible—Conjoint influence of the capillaries and absorbents in building up structure—Influence of the organic nerves on the process—Physical agent by which the organic nerves operate—Conclusion.
945. The object of the greater part of the processes hitherto described is to form the nutritive fluid, and to bring it to the requisite state of purity and strength. Recent researches into the composition of the nutritive fluid confirm the general correctness of the account already given of it, (211 et seq.).
946. When examined as it is flowing in the finest vessels of a transparent part of the body, or immediately after it is abstracted from the trunk of a vein or artery, before coagulation (218) takes place, the blood is seen to consist of a colourless fluid, through which is diffused a countless number of minute solid particles of a red colour. The colourless fluid is called the liquor sanguinis, and the solid particles the blood corpuscles or the red particles.
947. By the process of coagulation, the phenomena of which have been fully described (219 et seq.), the blood spontaneously separates into a clear fluid of a yellow colour called serum or blood-water, and into a solid mass termed the clot or the crassamentum. The serum, which must be carefully distinguished from the liquor sanguinis, is the fluid formed from the blood by coagulation; the liquor sanguinis is the fluid part of the blood which exists before coagulation.
948. The liquor sanguinis contains in solution a large quantity of animal matter, fibrin (228), which separates spontaneously in a solid form on coagulation; the serum also contains a quantity of animal matter in solution, albumen (224), which does not separate in a solid form spontaneously, but only on the application of heat, acids, alcohol, &c. (224). The animal matter, the fibrin, which separates spontaneously from the liquor sanguinis in a solid form, constitutes one part of the clot, and the other part of it consists of the red particles which floated in the liquor sanguinis.
949. Thus, by coagulation, the liquor sanguinis separates into a portion which remains fluid, the serum; and into a portion which becomes solid, the fibrin; while the fibrin, as it is passing from the fluid to the solid state, entangles the red particles, and both together form the clot; consequently the liquor sanguinis contains in solution two kinds of solid matter, fibrin and albumen; while the serum contains in solution only one kind of solid matter, albumen.
950. The solution of fibrin in the liquor sanguinis, and its spontaneous solidification during the process of coagulation, has been shown by Professor Müller in the following mode. Having carefully collected blood from the femoral artery of the frog, and also from the heart laid bare and incised, and having brought a drop of this pure blood under the microscope, and diluted it with serum, so that the red particles were separated from each other by distant intervals, he observed that there formed in those intervals a coagulation of previously dissolved matter, by which the separated red particles were connected together. By raising, with a needle, the coagulum occupying the intervening spaces, this solid matter was obtained free from red particles. The blood corpuscles of the frog are rendered, by a powerful microscope, so large, that this operation may be performed with the greatest distinctness. In consequence of the minuteness of the red particles of human blood they pass, with the liquor sanguinis, through filtering-paper; but those of the frog, being four times larger, are kept back by the filter, while the liquor sanguinis percolates through as a clear fluid, and then coagulates. This colourless coagulum is so transparent that it is not even detected, after its formation, until it is raised out of the fluid with a needle. It gradually thickens and becomes white. It is the fibrin of the blood in its purest state.
951. Professor Müller’s account of the structure of the red particles differs in a material point from that given (231 et seq.). He agrees that they are rounded bodies (fig. CXII. 1), generally of the same size, though some are seen larger than common, but never double the mean diameter; that they are always quite flat (232); that in a certain light they look as if they were hollowed out from the edges to the centre (fig. CXII. 1); but, he adds, “that this spot is a real depression, as some think, appears to me in the highest degree improbable; for I have at last convinced myself that the blood corpuscles of man and the mammalia contain a very small nucleus of the diameter of the flat corpuscle. My observations prove beyond doubt that the blood corpuscles of frogs and salamanders (fig. CXII. 4) contain a nucleus entirely different in its chemical relations from the outer layer. With one of Frauenhofer’s microscopes I have seen very distinctly, in the blood corpuscles of man an exceedingly small, round, well-defined nucleus, yellower and brighter than the transparent circumference. When the blood corpuscles are mixed, under the microscope, with acetic acid, the shell is almost entirely dissolved, and these small nuclei, which are seen with great difficulty in human blood, remain, while those of the frog appear, very evidently the nuclei observed earlier in the blood corpuscles. In man, the nuclei within the corpuscles are so small, that the diameter does not exceed the thickness of the flat corpuscles.”
952. The enveloping capsule is stated to be soluble in water, while the internal nucleus is insoluble; but the capsule is not soluble in serum; the albumen and the salts contained in the serum probably rendering it insoluble. The colouring matter of the capsule, which gives the red colour to the blood, is called hæmatosin. Lecanu considers the capsular substance as a combination of a specific colouring matter, which he calls globulin, and of albumen; but Müller regards it as fibrin, containing a quantity of iron. The latter physiologist states that the opinion of Brande, that the amount of iron in hæmatosin is not greater than in serum and other animal substances, has been refuted by Berzelius and Engelhart. The iron is not an accidental ingredient obtained from the food; for iron has been found in the blood of a new-born animal that has never even sucked. According to Berzelius the colouring matter of the blood contains a quantity of iron corresponding to somewhat more than a half per cent. its weight of metallic iron, and he thinks it most probable that the iron exists in the blood in the metallic state, and not as an oxide.