CHAP. II."| THE BLOOD. 31 



SEC. 2. THE LIQUOR SANGUINIS. FIBRIN AND ITS SUPPOSED 



PRECURSORS. 



The Liquor Sanguinis. 



Methods of It has already been stated that in the living 



obtaining Li- blood the corpusc i es fl oa t in a fluid termed the liquor 

 ouor San- 11 i 111 i 



guinis. sangmms or plasma, and that when blood coagulates it 



does so in consequence of the separation from the 

 plasma of a proteid substance termed fibrin. We have now to 

 describe the mode of obtaining liquor sanguinis, to describe fibrin, 

 to examine the bodies which the plasma contains, and to examine 

 the facts which relate to the separation from it of fibrin. 



Almost as soon as the liquor sanguinis is withdrawn from the 

 living vessels, it undergoes that change which results in the separa- 

 tion of fibrin and serum. The change may however be hindered by 

 various methods, which may be employed to furnish us with plasma 

 for examination. 



1. In order to obtain plasma in a state of great purity, blood 

 must be rapidly cooled to a temperature approaching that of melting 

 ice, at which temperature its coagulation is, as has been already 

 stated, deferred. 



The blood of most animals coagulates so rapidly that it is difficult 

 to cool any considerable quantity of blood to a temperature at which 

 coagulation would be long deferred, before the process has actually 

 occurred. The blood of the horse or donkey, however, usually 

 coagulates so slowly that with the aid of suitable contrivances con- 

 siderable quantities may be cooled to near C. before coagulation has 

 had time to occur ; and once at that temperature the process of co- 

 agulation may be long postponed. 



Under these circumstances the corpuscles sink pretty rapidly, 

 tending to form a sediment at the bottom of the vessel in which the 

 blood was received, and leaving an upper stratum of liquor sanguinis 

 perfectly free from red colour. The liquor sanguinis, decanted from 

 the corpuscles and exposed to a temperature favourable to coagula- 

 tion, exhibits the phenomena which have been described as character- 

 izing the coagulation of the blood, save that the coagulum is 

 colourless. If the fluid be stirred with twigs there will separate 

 from it stringy fibrin exactly similar to that obtained by similar 

 treatment from blood, save in the absence of colour derived from 

 entangled blood corpuscles. 



A convenient contrivance for collecting considerable quantities of plasma 

 from the blood of the horse is shewn in the annexed figure, and was sug 

 gested by Dr Burdon Sanderson ' . The apparatus consists of a vessel .with 



i Handbook for the Physiological Laboratory, p. 168. 



