FIBRIN. 355 



yielding substance, viz., diluting frogs' blood with sugared water, 

 (1 part of sugar to 200 of water,) and filtering it. 



The best means of obtaining frogs' blood for this experiment is 

 to amputate both thighs, and allow the blood, with which a consi- 

 derable quantity of lymph is mixed, to flow into sugared water, 

 which not only dilutes the liquor sanguinis, but retards the coagu- 

 lation of the fibrin ; the blood-corpuscles of the frog, like those of 

 most of the other amphibia, are, as is well known, much larger than 

 those of mammalia and birds, and therefore pass less easily through 

 the filter. 



A considerable quantity of the natural solution of fibrin may 

 be obtained from human blood (the corpuscles of which have the 

 property of sinking very rapidly), by pouring off the very slowly 

 coagulating fluid which collects above the blood-corpuscles. 



A single drop of fresh blood, when laid on the object stage and 

 covered with a piece of glass, is sufficient to exhibit the coagulation 

 of the fibrin under the microscope : on account of the mass of red 

 corpuscles the coagulation is however not so well seen as when we 

 employ a drop of fluid from the surface of blood, in which the red 

 corpuscles have sunk below the upper level. 



In preparing spontaneously coagulated and boiled fibrin, the 

 blood-clot must be cut into fine pieces, and then washed in water 

 until it appears perfectly white. The fibrin obtained in this manner 

 is more readily washed than when obtained from whipped blood. 

 The process of whipping consists either in shaking the blood, as it 

 flows from the veins, in a bottle with shot, or rapidly stirring it 

 with small twigs or rods ; the blood-corpuscles remain suspended 

 in the serum, while the fibrin separates in delicate but dense flakes; 

 the greater density of the small coagula renders it difficult, how- 

 ever, to wash away the blood-corpuscles enclosed in these flakes, or 

 to obtain the fibrin as free from hsematin as that which is obtained 

 from the blood-clot. In order to cleanse the fibrin as much as 

 possible, it is necessary, first to knead it for some time in water, 

 and then to hang it in water in a bag of linen, by which means the 

 salts and the pigment gradually dissolve, and the particles of the 

 fluid rendered thus heavier sink to the bottom of the vessel, while 

 pure water rises in their place. 



In order to obtain boiled fibrin in the greatest possible purity, 

 we must dry it after it has been boiled in w r ater ; it should be then 

 pulverised and extracted with alcohol containing sulphuric acid, 

 in order to remove any remains of pigment, and finally with ether 

 for the removal of the fat. 



2 A 2 



