1 8 A MANUAL OF VETERINARY PHYSIOLOGY 



coagulation in the remaining fluid can occur. The power of 

 spontaneous clotting lies, then, in the production of fibrin. 

 These changes may be graphically represented thus : 



On Clotting. 



(Plasma. {§«£; 



Blood. \ (Red. I r , , 



Corpuscles. \ White. ( Uot - 



I Blood platelets.J 





Plasma. 



When Whipped. 



/ Fibrin. 

 I Serum. 



Blood, i fRed. I Defibrinated 



White. | 



Blood platelets. J 



1 (Red. IDefibrmal 



Corpuscles. \ White. j blood. 



v I Blood platelets.J 



Fibrin is a yellowish-white, stringy-looking, bulky mass. Its 

 bulky appearance would lead to the belief that it exists in blood 

 in large quantities ; it is found, however, to be by weight rela- 

 tively small (o- 2 to 0-4 per cent.). 

 The cause of coagulation has kept physiologists busy for many 



I years, and even at the present time the matter has by no means 

 been settled. The theory most generally accepted is that of 



' Hammarsten — viz., that clotting is due to the conversion of a 

 fluid fibrinogen into a solid fibrin, under the influence of a sub- 



j stance spoken of as fibrin ferment. 



I If blood be prevented from coagulating, plasma can be obtained, 



and this plasma, depending upon the agents used in its pro- 

 duction, will teach the main facts of coagulation. If it be 

 obtained by cooling the blood, then the plasma will clot spon- 

 taneously by allowing the temperature to rise ; if the plasma be 

 obtained by previously mixing the blood with a definite amount 

 of magnesium sulphate or common salt, clotting will occur on 

 diluting it. If it be obtained by acting on blood with oxalates, 

 then clotting can be brought about on the addition of a lime salt. 

 The clot formed by the plasma coagulating is precisely the same 

 as that formed by the blood coagulating ; it is, of course, 

 colourless. 



If the above plasmas be acted upon by adding common salt to 

 half saturation, a precipitate of fibrinogen occurs ; this is a protein 

 belonging to the globulin group, and has previously been alluded 

 to. If this precipitate be redissolved by diluting the fluid, and 

 allowed to stand, it clots spontaneously. If a solution of pure 

 fibrinogen be prepared, it does not clot spontaneously, but it may 

 be made to do so by the addition of a drop of serum or the 

 washings of a blood-clot. 



