36 GENERAL ANATOMY. 



in pus. From the fact that cells exactly like the colorless corpuscles are being 

 constantly furnished to the blood by the lymphatic vessels and the chyle-ducts, 

 and also from their varying proportions in different parts of the circulation and 

 in different pathological conditions, the colorless corpuscles have been regarded 

 erroneously, however as an earlier stage of the colored blood-disks, but the 

 evidence in favor of this must be regarded as quite inconclusive. 



There can be no doubt that during embryonic life the red corpuscles are 

 developed from mesoblastic cells in the vascular area of the blastoderm. They 

 are at first nucleated and resemble white corpuscles, except in their color, and, 

 like them, are possessed of amoeboid movements. They are succeeded by smaller, 

 non-nucleated corpuscles, having all the characters of adult colored corpuscles, 

 probably formed by a conversion of the former into the latter. So that at birth 

 the nucleated red corpuscles have disappeared. In after life an important source 

 of the red corpuscles is the red marrow of bones, in which certain cells found in 

 the marrow are converted into colored blood-corpuscles by the loss of their nuclei, 

 and by their protoplasm becoming tinged with yellow. It is probable, also, that 

 the spleen may be a place for the formation of red corpuscles. This theory, which 

 was formerly universally believed, and was then discarded for the hypothesis that 

 the spleen was concerned in the destruction of the red corpuscles, has lately been 

 revived by Bizzozero. The question must still be regarded as sub judice. The 

 proportion of white corpuscles appears to vary considerably in different parts of 

 the circulation, being much larger in the blood of the splenic vein and hepatic vein 

 than in other parts of the body, while in the splenic artery they are very scanty. 



In addition to these corpuscles, a third variety is found in mammalian blood, 

 and has been specially studied and described by Hayem, Bizzozero, and Osier. 

 They are pale circular or oval disks, about one-quarter or one-third the size of the 

 red blood-corpuscles, and apparently contain no nucleus. They have been named 

 blood-plates or blood-plaques, and are supposed by Bizzozero to originate the fibrin- 

 ferment, and to be especially concerned in the coagulation of the blood. 



The liquor sanguinis or plasma is the fluid part of the blood, and contains in 

 solution various organic substances, such as jibrinogen, paraglobulin or serum 

 globulin, and serum albumen, together with certain salts, sugar, fatty matter, and 

 gases. Paraglobulin is probably contained partly in solution in the plasma, and 

 partly in the colorless corpuscles, and can be obtained by diluting the liquor san- 

 guinis with ten times its volume of ice-cold water, and then transmitting through 

 it a stream of carbon dioxide. Fibrinogen may be obtained in the same way as 

 paraglobulin, but the liquor sanguinis must be still further diluted and the current 

 of carbon dioxide must pass for a much longer time. Fibrin may be obtained 

 by whipping the blood, after it has been withdrawn from the body, with a bundle 

 of twigs, to which the fibrin, as it coagulates, adheres. Fibrin may also be 

 obtained by filtering the freshly-drawn blood of an animal whose corpuscles are 

 large, care being taken to retard coagulation as long as possible. Under these 

 circumstances the corpuscles are retained on the filter, and the liquor sanguinis, 

 passing through, coagulates and separates into fibrin, free from corpuscles, and 

 serum. 



Fibrin, thus obtained, is a white or buff-colored substance, presenting a 

 stringy appearance, and under the microscope exhibiting fibrillation. When 

 exposed to the air for some time, it becomes hard, dry, brown, and brittle. It is 

 a proteid compound, insoluble in hot or cold water, alcohol or ether. Under the 

 influence of dilute hydrochloric acid it swells up, but does not dissolve ; but when 

 thus swollen it is easily dissolved by a solution of pepsin. If heated for a- 

 considerable time in a solution of dilute hydrochloric acid, it gradually 

 dissolves. 



Serum is the fluid liquor sanguinis after the fibrin has been separated from it. 

 It is a straw-colored fluid having a specific gravity of 1.027, with an alkaline 

 reaction. Upon boiling it becomes solid, on account of the albumen which it 

 contains. It contains also salts, fatty matters, sugar, and gases. 



