THE BLOOD. 105 



226. To a little defibrinated blood in a test-tube 

 add an equal volume of water, and notice the change in 

 color, due to laking. 



227. Show that the blood can be laked by adding 

 a few drops of (a) ether, (b) chloroform, (c) solutions of 

 bile salts, (d) by freezing and thawing, (e) by heating to 

 65. 



228. To another portion add as much saturated salt 

 solution and observe that the color becomes brighter. 



229. Examine each of these under a microscope and 

 compare the appearance of the corpuscles with those of 

 the fresh blood. 



230. Place in a test-tube 5 to 10 cubic centimeters of a cold, 

 saturated solution of sodium sulphate. Open the carotid of a 

 rabbit or other small animal and allow twice as much blood to 

 flow into the tube. Collect as much more in a clean, perfectly dry 

 tube and allow both to stand twenty-four hours. In the first tube 

 there is no coagulation, but the corpuscles settle toward the bot- 

 tom. In the second the corpuscles are mostly held in the mass of 

 coagulated fibrin from which drops of serum are pressed out. 



231. Place in a beaker or flask 3 to 4 cubic centimeters of a 

 4-per-cent. solution of neutral potassium oxalate. Insert a 

 cannula into the carotid artery of a rabbit or cat and let 10 

 times the above volume of blood flow into the solution without 

 first coming into contact with the glass. Let it stand in a cool 

 place or whirl it in a centrifuge until the corpuscles have settled. 

 The clear liquid above is oxalate plasma. Pour it into a test- 

 tube and notice that it does not clot. Add a few drops of calcium 

 chlorid solution when a clot forms. (Compare this with the ac- 

 tion of remain.) 



232. From the oxalate plasma precipitate the fibrinogen 

 with an equal volume of saturated salt solution. Apply to it the 

 protein reactions. 



233. Notice that the serum does not clot with calcium 

 chlorid. Why not? 



