Human physiology / by John Thornton.

  • Thornton, John
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Human physiology / by John Thornton. Source: Wellcome Collection.

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    sists of a fine network of fibrin fibrils, in the meshes of which are entangled the red and white corpuscles of the blood. Fibrin is thus formed from the blood-plasma of living blood, and the clot or crassamentum consists of filaments of fibrin with the blood-corpuscles entangled in its meshes. The interior of the clot is darker and firmer than the outside. Serum is plasma minus fibrin or the elements of fibrin. Human blood becomes viscid in two or three minutes, forms a jelly five or six minutes later, produces serum in a few more n)inutes, the clot con- tinuing to shrink for several hours. By surrounding freshly drawn blood with a freezing mixture coagulation is delayed, the heavier red corpuscles sink towards the bottom, and the lighter white corpuscles that do not disintegrate remain near the top. On removing the blood from the influ- ence of the low temperature, coagulation occurs, and the clot that forms has its upper portion formed of whitish fibrin and colourless corpuscles only. This pale upper layer is termed the btiffy coat. The blood of the horse and inflammatory blood generally coagulates slowly and forms a buffy coat. Blood does not clot during life in the uninjured blood-vessels, as the living tissue of the inner coat either prevents the formation of the fibrin * ferment' that changes the fibrinogen of the plasma into fibrin or removes Fig. 64. —Diagram to illustrate the Process of Coagulation. I. Fresh. II. Coagulating. III. Coagulated. (Corpuscles and plasma.) (Birth of fibrin.) (Clot and serum.) Plasma minus fibrinogen equals serum Corpuscles plus fibrin equal clot. the ferment body as soon as it is formed. Injury to the inner coat of the blood-vessels may produce coagulation within the vessels. Both red and white corpuscles are specifically heavier than the plasma (the red are heavier than the white), and hence if shed blood be kept from coagulation, as may be done by surrounding horse's blood with a mixture of ice and salt, the corpuscles have time to sink almost com- pletely, and plasma may thus be obtained separately. Such plasma, under favourable conditions, coagulates in the same manner as the entire blood, first forming a jelly and then separating into a colourless shrunken clot and serum. The corpuscles, therefore, are not an essential part of the clot, though it is possible, as the colourless corpuscles especially begin to disintegrate in shed blood, that the corpuscles play some part in the act of coagulation. Indeed, the theory of coagulation now generally held is thus stated by Halliburton :—' When the blood is within the vessels, one of the constituents of the plasma, a proteid of the globulin class called fibrinogen, exists in a soluble form. When the blood is shed, fibrinogen is converted into the comparatively insoluble substance, fibrin. This change is brought about by the activity of a special un- organised ferment, called the fibrin-ferment. This ferment does not exist in healthy blood contained in healthy blood-vessels, but is one of the products of the disintegration of the white corpuscles, and probably also of
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