294 THE BLOOD. [cHAP.xxvn. 



is also favoured by spreading out the blood on a flat surface; 

 and, within certain limits, by an increase of the fluid parts of the 

 blood. 



On the other hand, coagulation is retarded by the addition of 

 alkalies, and some of their salts, as sulphate of soda, nitrate of soda, 

 carbonate of soda, chloride of sodium; also carbonate of potass, 

 nitrate of potass, and nitrate of lime. A strong solution of any 

 of these salts, added to fresh drawn blood, will delay or stop 

 its coagulation according to the strength and quantity of the 

 solution. 



Authors affirm that the blood will not coagulate in the bodies of 

 animals killed by blows on the epigastrium, or after having been 

 long hunted, or by electricity or lightning. It will not coagulate 

 after asphyxia by carbonic acid, as in the following cases, recorded 

 by Mr. Gulliver : A man, setat. thirty-five, and three children, 

 were suffocated in a burning house, their bodies being untouched 

 by the fire : in all of them the blood was fluid, forty-eight hours 

 after death, in the heart and great vessels, and did not coagulate 

 after its removal out of the body. 



The coagulation of the blood appears to be retarded by its con- 

 tact with living surfaces. Thackrah's experiments showed that 

 blood confined between two ligatures in living vessels, remained 

 fluid for a considerable time, from five to sixty minutes ; F. Simon 

 affirms that it will retain its fluidity for three hours : and experi- 

 ments of the same kind by Hewson, lead to the conclusion that the 

 coagulation is retarded under similar circumstances. Fluids with- 

 drawn from serous cavities, as in ascites or hydrocele, often exhibit 

 a coagulum of considerable size, which does not form till some 

 minutes after their removal, showing that the fibrine must have 

 been prevented from coagulating so long as it remained in the 

 living body. 



The addition of bile retards or prevents coagulation, probably by 

 the mechanical obstacle which it affords to the cohesion of the par- 

 ticles of fibrine. According to John Hunter, the addition of a 

 solution of opium to the blood retards its coagulation. 



It is needless to waste time in inquiring into the cause of coagu- 

 lation. That the phenomenon belongs only to one of the constituents 

 of the blood, is proved unequivocally by the fact, that if that ma- 

 terial, the fibrine, be removed by whipping blood with a bunch of 

 twigs, as it flows from a vein, coagulation will not take place in the 

 fluid which remains. The fibrine has accumulated in a coagulated 

 state round the twigs, and the fluid received into the vessel consists 



