178 THE BLOOD. 



This vessel is not only surrounded with ice externally, but 

 contains in its axis a smaller cylinder, closed at its lower end, 

 which is also filled with ice. Between the external surface of 

 the smaller cylinder and the internal surface of the larger, 

 there is an interval which does not exceed half an inch in 

 width, so that the whole of the liquid which occupies it is kept 

 at freezing temperature. In the course of two hours or less 

 the blood has separated into two layers, of which the lower 

 contains all the corpuscles. The upper stratum consists 

 entirely of plasma a liquid which, in its general aspect, 

 resembles ordinary serum, but is not so transparent. The 

 most obvious as well as the most important property which it 

 possesses is that of coagulation. So long as it is kept at C. 

 it remains liquid ; but if the temperature is allowed to rise 

 even a few degrees above freezing point, the whole mass is 

 converted into a gelatinous clot. 



3. Experiments Illustrative of the Properties of 

 Plasma and Fibrin. 1. Transfer some of the plasma, with 

 the aid of a cooled pipette, to a small narrow test glass, 

 surrounded with ice and water contained in a small beaker. 

 As the ice gradually wastes, the liquid becomes gelatinous. 

 The surface by which the mass adheres to the glass is so 

 extensive as compared with its volume, that the adhesion is 

 permanent. Consequently, if the tube is examined after 

 having been left to itself for several hours, it is found that 

 the plasma has not (as in other cases of coagulation) separated 

 into clot and serum, but that it appears to be entirely semi- 

 transparent and gelatinous. 



2. Another quantity of plasma is allowed to coagulate in a 

 wide vessel. At first the process seems to go on in a similar 

 manner, and for a time the mass adheres to the sides of the 

 vessel. Afterwards, as it contracts, drops of serum collect, 

 first on the surface, then between the clot and the sides of the 

 glass. Soon the clot detaches itself wholly from the vessel, at 

 the same time diminishing in volume. Eventually we have a 

 clear liquid (serum) in which an opaque white cast of the 

 beaker floats. As, in consequence of the adhesion of the 

 coagulum to the sides, contraction is more resisted in the 

 horizontal direction than in the vertical ; the upper surface 

 always becomes more or less concave. 



3. Preparation of Fibrin. a. The clot from 2 is removed 

 from the liquid, divided into small fragments, and washed with 

 water until it is absolutely colorless. In this condition it 

 differs strikingly from the semi-transparent gelatinous mass 

 which is obtained in 1. It is dense, fibrous, and opaque, and 

 extremly elastic. b. A fresh portion of plasma is briskly 

 agitated with a rod of whalebone or other suitable implement. 

 In this case the fibrin is obtained in fine fibres, which may also 



