40 



blood due to the withdrawal of the hemoglobin from the red 

 corpuscles into the water. Test the transparency by look- 

 ing at some printed matter through this blood as in 187. 



189. To 2 cc. of defibrinated blood in a test-tube add 5 

 volumes of a 10% solution of sodium chloride. It changes 

 to a very bright, florid, brick-red color. Compare its color 

 with No. 188. 



190. Place a watery solution of defibrinated blood in a 

 parchment tube, and suspend in a vessel of distilled water. 

 After several hours note that no hemoglobin has passed into 

 the water. Test the diffusate for chlorides with silver nitrate 

 and nitric acid. Hemoglobin does not dialyze, although it 

 is crystallizable. 



191. Put a drop of blood on a slide. Heat it gently over 

 a flame, so as to evaporate the water. Then add a small 

 crystal of common salt and a drop of glacial acetic acid ; 

 put on a cover-glass, and again heat slowly till the liquid 

 just begins to boil. Take the slide away from the flame for 

 a few seconds, then heat it again for a moment, and repeat 

 this process for two or three times. Now let the slide cool 

 and examine with the microscope (high power). The small 

 black or brownish-black crystals of hemin will be seen. 

 This test is often important in some medico-legal cases 

 where only a trace of blood is available for examination. 

 If the blood stain be upon a piece of cloth, it may be soaked 

 in a little distilled water and examined by the spectroscope 

 or micro-spectroscope. The liquid may then be evaporated 

 to dryness on the water bath and the hemin test made. Or 

 perform the hemin test directly on the piece of cloth. 



192. In the blood saved for clotting, note that in a few 

 minutes the blood congeals, and when the vessel is tilted 

 the blood no longer moves as a fluid, but as a solid. After 

 an hour or so, pale yellow colored drops of fluid — the serum 

 — are seen on the surface, having been squeezed out of the 

 red mass, the latter being the clot and consisting of fibrin 

 and red corpuscles. 



