258 



THE BLOOD. 



Fig. 87. 



constitution of the circulating fluid, since it is upon its power of spon- 

 taneous solidification that the coagulability of the entire blood depends. 

 This process takes place, under all ordinary conditions, soon after the 

 blood has been withdrawn from the circulation ; and the fibrine may be 

 obtained in a state of tolerable purity by continuously stirring freshly- 

 drawn blood with glass rods or a bundle of twigs. When coagulation 

 occurs, the fibrine solidifies in the form of thin layers adherent to the 

 surface of the rods or twigs. It at first contains, entangled with' it, 

 some of the red globules of the blood with their coloring matter ; but 

 these, as well as other foreign substances, may be removed by subjecting 

 the mass for a few hours to the action of running water. The fibrine 

 then presents itself under the form of nearly white threads and flakes, 

 having a semi-solid consistency and a considerable degree of elasticity. 

 Coagulated fibrine, if examined in thin layers, is seen to have a fibroid 

 or filamentous texture. The filaments of which it is composed are 



colorless and elastic, and when 

 isolated are seen to be exceed- 

 ingly minute, being not more 

 than 0.5 mmm. in diameter. 

 They are partly so placed as to 

 lie parallel with each other, and 

 this is probably their arrange- 

 ment throughout the undis- 

 turbed fibrinous laj^er; but 

 when torn up for microscopic 

 examination, its filaments are 

 seen to be in many spots inter- 

 laced with each other in a kind 

 of irregular network. On the 

 addition of dilute acetic acid 

 the filaments become swollen, 

 transparent, and fused into a 

 homogeneous mass, but do not 

 dissolve. They are often in- 

 terspersed with minute granules, which render their outlines more or less 

 obscure. 



Once coagulated, fibrine is insoluble in water and can only be again 

 liquefied by the action of an alkaline or strongly saline solution, by pro- 

 longed boiling at a very high temperature, or by digesting with gastric 

 juice or an acidulated solution of pepsine. These agents, however, pro- 

 duce a permanent alteration in the properties of the fibrine, and after 

 being subjected to their influence it is no longer the same substance as 

 before. 



The quantity of fibrine which may be extracted from the blood varies 

 in different parts of the body. According to most observers, venous 

 blood in general yields less fibrine than arterial blood. A portion of it 

 therefore disappears in passing through the capillary circulation. In 



COAGULATED FIBRINE, showing its flbrillatod 

 condition. 



