30 THE BLOOD. 



It is a curious fact that leech-drawn blood remains fluid in the body of the ani- 

 mal. Richardson has observed, also, that the blood flowing from a leech-bite presents 

 the same persistent fluidity, which explains the well-known fact that the insignificant 

 wound gives rise to considerable haemorrhage. On this point he has made the following 

 curious experiment : 



" After the leech was removed from the arm, the wound it had produced continued 

 to give out blood very freely. I caught the blood thus flowing at different intervals, 

 allowing it to trickle into teaspoons of the same size and shape. The results were curi- 

 ous. The blood which was received into the first spoon, and which was collected imme- 

 diately after the removal of the leech, was dark, and showed the same feebleness of 

 coagulation as the blood taken from the leech itself. Another portion of blood, received 

 into a second spoon five minutes later, coagulated in twenty-five minutes with moderate 

 firmness. A third portion of blood, caught ten minutes later still, coagulated in eight 

 minutes ; while at the end of half an hour the blood which still flowed from the wound 

 coagulated firmly, and in fine red clots, in two minutes. Ultimately the blood coagu- 

 lated as it slowly oozed from the wound, so that the wound itself was sealed up." 



The existence of projections into the caliber of vessels, or the passage of a fine thread 

 through an artery or vein, will determine the formation of a small coagulum upon the 

 foreign substance, while the circulation is neither interrupted nor retarded. These facts 

 demand explanation ; but all we can say with regard to them is, that, in the present 

 state of our knowledge, explanation is difficult, if not impossible. The process, under 

 these circumstances, cannot be subjected to direct experiment, as in the case of blood 

 coagulating out of the body ; but a reasonable inference is that the foreign substance 

 arrests the circulation of a certain portion of plasmine, which then undergoes decompo- 

 sition. 



During coagulation, fibrin assumes a filamentous form, presenting, tinder the micro- 

 scope, the appearance of rectilinear fibrillse. These fibrilloa gradually increase in num- 

 ber and, as contraction of the clot occurs, becomes irregularly crossed. They are always 



FIG. 8. Coagulated fibrin. (Kobin.) 



Fibrinous clot, without red corpuscles, and containing leucocytes, thrown off in the form of a whitish pseudo-mem- 

 brane in a case of ulceration of the neck of the uterus with haemorrhage. 



straight, however, and never assume the undulating appearance characteristic of the 

 white fibrous tissue. The appearance just described does not indicate a process of or- 

 ganization. When fibrin is effused into any of the tissues or organs from rupture of 

 vessels, it acts as a foreign substance, and, in time, becomes entirely or in part absorbed, 

 The gradual production of membranes of new formation, as one of the results of inflam- 

 mation, these becoming organized, is entirely different from sudden haemorrhagic 

 effusions. 



The blood of the renal and hepatic veins, capillary blood, and the blood which passes 



