THE CIRCULATION. 105 



est injury in drawing blood would prove fatal. Whereas 

 now, in vastly the larger proportion of cases, bleeding 

 ceases spontaneously, because the blood, as it coagulates, 

 stops the mouths of the injured blood-vessels. In another 

 class of cases, where larger vessels are cut or torn, it is 

 simply necessary to close them by a temporary pressure ; 

 for in a few minutes the clot will form and seal them up. 

 In still more serious cases, where the blood-vessel is of 

 large size, the surgeon is obliged to tie a " ligature'' about 

 it, and thus prevent the force of the blood-current from 

 washing away the clots, which, forming within and around 

 the vessel, would close it effectually. 



11. It is worthy of remark that this peculiarity is early 

 implanted in the blood, even before birth, and in advance 

 of any existing necessity for it; thus anticipating and 

 guarding against danger. But this is not all. Of most 

 of the inferior animals, which, as compared with man, are 

 quite helpless,*the blood coagulates more rapidly, and in 

 the case of the birds, almost instantly. The relative 

 composition of fluid and coagulated blood may be thus 

 *< ^resented : 



Fluid Blood. Coagulated Blood. 



Plasma;.... Serum Serum 



-Fibrin - .... 

 Corpuscles Corpuscles ...'-^-..Clot. 



12. The Uses of the Blood. The blood is the great 

 provider and purifier of the body. It both carries new 

 materials to all the tissues, and removes the worn out par- 

 ticles of matter. This is effected by the plasma. It both 

 conveys oxygen and removes carbonic acid. This is done- 

 through the corpuscles. Some singular experiments have 



1 1 . What is worthy of remark ? Coagulation of the blood of inferior animals ': 

 Of the blood of birds ? 



12. The blood, as a provider and purifier? What uses does the blood sub- 

 serve ? Experiments ? Transfusion ? 



5* 



