THE BLOOD-PLASMA AND ITS RELATION TO THE SERUM. 65 



THE BLOOD-PLASMA AND ITS RELATION TO THE SERUM. 



The unmodified fluid of the blood is known as plasma. In this, how- 

 ever, there separates, generally soon after escape of the blood from the 

 vessels, a nbrillated substance, namely fibrin. After this separation, 

 the remaining clear fluid, which no longer undergoes coagulation spon- 

 taneously, is known as serum. The plasma is a clear, transparent, 

 somewhat consistent fluid, which in most animals is almost colorless, 

 but in human beings is yellowish and in the horse of citron-yellow 

 color. 



DEMONSTRATION OF PLASMA. 



(A) Without admixture. As plasma cooled to a temperature of o C. does 

 not undergo coagulation, the blood flowing from a vein particularly of the horse, 

 which is peculiarly suitable on account of the slowness of coagulation and the 

 rapidity with which sedimentation of the blood-corpuscles takes place-; is received 

 into a narrow, graduated cylinder standing in a cold mixture. In the blood, 

 which remains fluid, the erythrocytes sink to the bottom within a few hours, and 

 the plasma forms above a clear fluid, which can be removed with a cooled pipet. 

 If this is further passed through a filter upon an ice-cold funnel the plasma will 

 also be freed from leukocytes. 



The amount can be read from the graduated cylinder, but only approximately, 

 because of the presence of plasma between the sedimented corpuscles. If heated, 

 the plasma, in so far as it contains leukocytes, is transformed, through the forma- 

 tion of fibrin, into a tremulous jelly. If, however, it be whipped with a rod the 

 fibrin will be obtained as a stringy mass. Plasma free from leukocytes is not 

 capable of coagulation. 



If the amount of fibrin in a volume of plasma isolated by whipping (varying 

 between 0.7 and i.o per cent.) and in the same manner the amount in a volume 

 of blood be determined the two results afford a basis for estimating the amount 

 of plasma in the blood. 



(B) With saline admixture. If the blood flowing from a vein into a graduated 

 cylinder be mixed with agitation with } volume of concentrated solution of 

 sodium sulphate or with a 25 per cent, solution of magnesium sulphate 

 (i volume to 4 volumes of blood), the cells sink to the bottom in a cool place, 

 while the clear supernatant saline plasma, which can be measured, is pipetted off. 

 If the salt be removed from the plasma by means of the dialyzer coagulation 

 takes place. The same result is brought about by dilution with water. 



FIBRIN: ITS GENERAL PROPERTIES; COAGULATION. 



Fibrin is the substance that brings about coagulation in shed blood 

 as well as in plasma and likewise in lymph, and in the chyle, by 

 solidification. If the fluids mentioned are placed at rest and left to 

 themselves the fibrin forms innumerable microscopically delicate (Fig. 9) 

 doubly refracting filaments, which hold the blood-cells together like 

 a spider's web, and with the cells form a mass of gelatinous consistency 

 that is known as blood-clot (placenta sanguinis}. At first this is quite 

 diffluent and it is only in the course of from two to fifteen minutes that 

 a number of filaments appear upon the surface that can be removed with 

 a needle, while the interior of the blood-mass is still liquid. In a short 

 time the filaments extend throughout the entire mass. The blood in 

 this stage of coagulation has been designated cruor. Later, in the 

 course of from twelve to fifteen hours, the threads of fibrin contract 

 more and more firmly about the corpuscles, and there then results the 

 more solid, gelatinous, tremulous substance, which can be cut with a 

 knife, and which has expressed a clear fluid, known as blood-serum 

 (serum sanguinis}. The blood-clot takes the shape of the vessel in which 

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