30 CIRCUMSTANCES WHICH RETARD COAGULATION. [BOOK T. 



The following is the best method of exhibiting this fact for purposes 

 of class demonstration : 



A small platinum crucible, or still better, as permitting more easily of an 

 examination of its contents, a small platinum basin is immersed in a vessel 

 containing a mixture of ice and salt ; a frog is then decapitated, and the 

 blood is allowed to flow into the frozen vessel, where it instantly congeals. 

 The platinum vessel can be taken out of the ice and held up so as to shew 

 the hard frozen drops of blood. The experimenter then places the vessel on 

 the palm of his hand, the heat of which almost instantly thaws the blood, 

 which can then be dropped into a watch-glass. The platinum vessel 

 is again placed on the ice and the thawed blood transferred to it, to be 

 frozen a second time. This freezing, thawing, and transference from one 

 vessel to another may be repeated several times ; at last the blood is 

 allowed to remain in the watch-glass, when after a few minutes it sets into 

 a firm jelly. 



b. Contact with the living tissues. 



If a vein be exposed and ligatures be applied to it so as to 

 confine a quantity of blood within it, and it be then cut out of the 

 body, it will be found that on opening the vein after an hour the 

 blood will still be fluid, though after contact with foreign matter it 

 will coagulate in a few minutes (Hunter 1 , Hewson 2 ). For some hours 

 after somatic death the blood remains fluid in all vessels except the 

 heart and principal trunks, provided that the vessels have been pre- 

 viously healthy. Blood will remain fluid for hours in a vein after 

 being exposed with the utmost freedom to the air by being poured 

 in a thin stream from one vein to another (Lister 3 ). 



c. The addition of a sufficient quantity of sodium chloride, 

 sodium sulphate, potassium nitrate or some other neutral salts 

 (Hewson 4 , Davy 5 ), will prevent coagulation, which will however 

 occur subsequently if a sufficient quantity of water be added. 



Thus to quote Hewson's own words, " if six ounces of human blood 

 are received from a vein upon half an ounce of true Glauber's salt 

 reduced to a powder, and the mixture agitated so as to cause the 

 salt to be dissolved, that blood will not coagulate on being exposed 

 to the air, as it would have done without the salt ; but if to this 

 mixture about twice its quantity of water be added, in a short time 

 the whole will be jellied or coagulated, and on shaking the jelly, 

 the coagulum will be broken, and the part so coagulated can now be 

 separated as it falls to the bottom and proves to be lymph" (i.e. fibrin). 



1 Hunter's Works, by Palmer, Vol. in., p. 29. 



2 Hewson's Works, p. 22. 



3 Lister, "On the Coagulation of the Blood ;" the Croonian Lecture for 1863. Pro- 

 ceedings of the Royal Society, Vol. xn. p. 580. 



4 Hewson, op. cit., p. 11 et seq. 



* Davy, Researches, Vol. n. 101-2. 



