22 CHEMICAL PHYSIOLOGY. 



vessel, and allow it to coagulate. Set it aside for two days, 

 and then observe the serum and the clot. Pour off the 

 pale, straw-coloured serum, and note the red clot, which has 

 the shape of the vessel, although it is smaller than the latter. 



(B.) If the blood of a horse can be obtained, study it, 

 noting that the upper layer of the clot is paler in colour ; 

 this is the buffy coat. 



9. Circumstances influencing Coagulation. 



Effect of Cold. Place a small platinum basin a brass or 

 glass thimble will do quite well on a freezing mixture of ice 

 and salt, decapitate a frog or rat, and allow the blood to flow 

 directly into the cooled vessel. At once it becomes solid or con- 

 geals, but it is not coagulated. As soon as the blood becomes 

 solid, remove the thimble and thaw the blood by placing it on the 

 warm palm of the hand, when the blood becomes fluid, so that it 

 can be poured into a watch-glass; if the vessel be once more 

 placed on the freezing mixture, the blood again congeals and 

 solidifies, and on its being removed becomes fluid. Observe at 

 the same time that the colour of the blood changes, becom- 

 ing darker and transparent. This is the laky condition due 

 to the discharge of the haemoglobin from the corpuscles. Place 

 the vessel with the fluid blood on the table, and it clots or forms 

 a firm jelly. 



10. Influence of Neutral Salts on Coagulation. Take to the 

 slaughter-house a vessel capable of holding 500 cc., but previously 

 place in it 170 cc. of a saturated solution of sodic sulphate or 

 magnesic sulphate. Allow enough blood from an animal to run 

 into the saline solution to fill the vessel, and mix them thoroughly. 

 The blood does not clot but remains fluid. Place the vessel 

 aside on ice, and note that the corpuscles subside, leaving a clear 

 yellowish layer on the surface the plasma mixed with the saline 

 solution, and known as salted plasma. 



(a.) Pipette off the salted plasma use 2 cc. add to it 

 3 to 5 volumes of water, and observe that it clots after 

 a time. The clotting is hastened by the action of gentle heat. 



In laboratories where a centrifugal apparatus is in use, the 

 corpuscles can be rapidly separated from the plasma, and 

 enough of the latter obtained for the purposes of a large 

 class of students. 



