22-i THE BLOOD. 



filaments of which it is composed are colorless and elastic, and when 

 isolated are seen to be exceedingly minute, being not more than 

 4tio(j or even 5 (j no IT f an mcn i* 1 diameter. They are in part 

 arranged so as to lie parallel with each other ; but are more gene- 

 rally interlaced in a kind of irregular network, crossing each other 

 in every direction. On the addition of dilute acetic acid, they swell 

 up and fuse together into a homogeneous mass, but do not dissolve. 

 They are often interspersed everywhere with minute granular mole- 

 cules, which render their outlines more or less obscure. 



Once coagulated, fibrin is insoluble in water and can only be 

 again liquefied by the action of an alkaline or strongly saline solu- 

 tion, or by prolonged boiling at a very high temperature. These 

 agents, however, produce a complete alteration in the properties of 

 the fibrin, and after being subjected to them it is no longer the 

 same substance as before. 



The quantity of fibrin in the blood varies in different parts of the 

 body. According to the observations of various writers, 1 there is 

 more fibrin generally in arterial than in venous blood. The blood 

 of the veins near the heart, again, contains a smaller proportion of 

 fibrin than those at a distance. The blood of the portal vein con- 

 tains less than that of the jugular ; and that of the hepatic vein less 

 than that of the portal. 



The albumen is undoubtedly the most important ingredient of the 

 plasma, judging both from its nature and the abundance in which 

 it occurs. It coagulates at once on being heated to 160 F., or by 

 contact with alcohol, the mineral acids, the metallic salts, or with 

 ferrocyanide of potassium in an acidulated solution. It exists natu- 

 rally in the plasma in a fluid form by reason of its union with 

 water. The greater part of the water of the plasma, in fact, is in 

 union with the albumen ; and when the albumen coagulates, the 

 water remains united with it, and assumes at the same time the 

 solid form. If the plasma of the blood, therefore, after the removal 

 of the fibrin, be exposed to the temperature of 160 F., it solidifies 

 almost completely ; so that only a few drops of water remain that 

 can be drained away from the coagulated mass. The phosphates 

 of lime and magnesia are also held in solution principally by the 

 albumen, and are retained by it in coagulation. 



The fatty matters exist in the blood mostly in a saponified form, 

 excepting soon after the digestion of food rich in fat. At that 

 period, as we have already mentioned, the emulsioned fat finds its 



Robin and VerJeil, op. cit., vol. ii. p. 202. 



