INTRODUCTION.
The blood is a fluid tissue composed of cells floating in an albuminous plasma, and it differs from other tissues not less in the arrangement of its elements than in the activity of the changes which go on in it. It is the mart into which is poured from the alimentary canal the commodities needed in nutrition, and the elements of the body select from it the various materials which they require, giving in exchange those chemical combinations which result from the metabolism of the tissues. In spite of ceaseless changes, a uniformity of composition is one of the most striking features of the blood in health. This is maintained, as regards the constituents of the plasma, by the activity of the organs which regulate income and expenditure—the alimentary canal and liver on the one hand, and the kidneys, lungs, and skin on the other; while histological uniformity is maintained by the adenoid or cytogenous tissue throughout the body, the function of which is to replace the wornout blood-corpuscles.
The corpuscles form rather less than one-half by weight of the blood. The plasma contains about 90 per cent. of water, which holds in solution proteids in the form of serum, albumen, and the fibrin-forming factors; sugar in traces; creatin, hypoxanthin, and urea; various fatty bodies in small amount; salts, chiefly sodium; and gases. The corpuscles (red) consist of hæmoglobin (90 per cent.), proteid bodies, and traces of lecithin and cholesterin.
So far as we know at present of the function of these two portions of the blood, the plasma ministers to the general nutrition of the tissues, while the corpuscles (red) are chiefly concerned with respiratory processes, acting as the carriers of oxygen and carbonic oxide.
We shall first give a brief account of the histological characters of the blood, and of the relation of the groups of adenoid or cytogenous tissue to the corpuscles.
Two forms of corpuscles are usually described, but we can recognize four varieties of blood-corpuscles in the body: (1) red, (2) white, (3) nucleated red, and (4) the hæmatoblasts (Hayem), or blood-plates of Bizzozero.
(1) Red Corpuscles.—In each cubic millimeter of plasma there are about 5,000,000 red cells. The percentage may vary within health limits from 90 to 110. The corpuscles are circular, non-nucleated, biconcave disks, homogeneous, to ordinary inspection structureless, and consist of a colorless stroma which is possibly reticulated, and a red coloring matter, the hæmoglobin. In health they are tolerably uniform in size, about 7.9 µ1 in diameter, or in English measurement 1/3200 of an inch (Gulliver). Even in normal blood there may be slight variations in size between 6.5 µ and 8.5 µ, the average, according to Hayem, being 7.5 µ.
1 µ is used to signify a micro-millimeter or 1/1000 part of a millimeter.
(2) Colorless or white corpuscles, nucleated masses of protoplasm, with an average diameter of 10 µ, or about 1/2500 of an inch. The majority have a finely granular protoplasm, but in a few the granules are coarse and do not completely fill the clear protoplasm. The ultimate structure is reticular (Heitzman). Erhlich2 has shown by their varying reaction to eosin that there are chemical differences among the colorless cells quite unrecognizable by other means. In healthy blood they display active amoeboid changes at ordinary temperatures. Their protoplasm does not, as is commonly stated, rapidly disintegrate, but if kept at a medium temperature retains its vitality, as shown by movements, for hours. The number per cubic millimeter is from 8 to 15 millions, and the ratio to the red is variously computed as 1 to 300 or 1 to 500.
2 Frerichs find Leyden's Archiv, Bd. i.