Читать книгу The Body at Work: A Treatise on the Principles of Physiology онлайн

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The peculiar construction of the splenic pulp which brings the blood more or less to rest within its sponge-work, and the transmission to the liver of the blood which leaves the spleen, indicate that it is an organ in which blood itself receives some kind of treatment. It is not passed through it, as it is through all other parts of the body, in closed pipes. The spleen is a reservoir, or a filter-bed, into which blood is received.

Fig. 5.—A Minute Portion of the Pulp of the Spleen,

very highly magnified.

Stellate connective-tissue cells form spaces containing red blood-corpuscles and leucocytes. In the centre of the diagram is shown the mode of origin of a venule. It contains two phagocytes—the upper with a nucleus, two blood-corpuscles just ingested, and one partially digested in its body-substance; the lower with two blood-corpuscles.

The red blood-corpuscles of mammals are cells without nuclei, and with little, if any, body-protoplasm. They are merely vehicles for carrying hæmoglobin. We should deny to them the status of cell, if it were possible to prescribe the limit at which a structural unit ceases to be entitled to rank as a cell. They are helpless creatures, incapable of renewing their substance or of making good any of the damage to which the vicissitudes of their ceaseless circulation render them peculiarly liable. It is impossible to say with any approach to accuracy how long they last, but probably their average duration is comparatively short. The spleen is a labyrinth of tissue-spaces through which at frequent intervals all red corpuscles float. If they are clean, firm, resilient, they pass through without interference. If obsolete they are broken up. In the recesses of the spleen-pulp, leucocytes overtake the laggards of the blood-fleet, attach their pseudopodia to them, draw them into their body-substance, digest them. The albuminous constituent of hæmoglobin they use, presumably, for their own nutrition. The iron-containing colouring matter they decompose, and excrete in two parts; the iron (perhaps combined with protein); the colouring matter, without iron, as the pigment, or an antecedent of the pigment, which the liver will excrete in bile. Hæmoglobin is undoubtedly the source of bilirubin, and general considerations lead to the conclusion that it is split into protein, iron, and iron-free pigment in the spleen; but the details of this process have never been checked by chemical analysis. Neither bile-pigment nor an iron compound can be detected in the blood of the splenic vein. The only evidence of the setting free of iron in the spleen is to be found in the fact that the spleen yields on analysis an exceptionally large quantity of this metal (the liver also yields iron), and that the quantity is greatest when red corpuscles are being rapidly destroyed.