78 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



2. Examination of Suspected Blood. Dissolve a small quantity of 

 the suspected blood in normal saline solution. Search for corpuscles 

 and apply the hemin test. Dissolve a small portion of the same ma- 

 terial in water or in a dilute solution of caustic soda or potash and make 

 a spectroscopic examination as described in the preceding paragraphs. 



Annotation. The student should at this time be shown the lytic and precipitin 

 reactions of blood-sera. Since it often takes several weeks to sensitize an animal, 

 these tests for blood cannot be performed by students individually. 



3. Hemin Crystals. Place a drop of blood upon a glass slide and 

 dry it slowly in the gas flame. Add a few crystals of sodium chlorid and 

 a drop of glacial acetic acid. Cover and gently heat until bubbles of 

 gas are given off. Hemin crystals appear as minute, dark brown, 



FIG. 48. DIAGRAM OF SPECTROSCOPE. 



rhombic crystals which cannot well be confounded with the irregular 

 colorless crystals frequently seen in preparations of this kind. 



4. Blood Crystals. Mix a drop of rat's blood on a slide with a drop 

 of water. After about five to ten minutes crystals of oxyhemoglobin 

 will be seen to form. 



5. Chemical Tests for Blood. Add a small quantity of blood to 

 tincture of guaiacum. Add a little hydrogen peroxid to this mixture. 

 The blue color ensuing is due to the iron-containing radical in hemo- 

 globin. Repeat this test with blood which has been boiled. The same 

 reaction results. 



Dilute a little blood until practically colorless. Add to it a few 

 drops of benzidin dissolved in glacial acetic acid and a few drops of 

 hydrogen peroxid. A blue color develops. Repeat this test with blood 

 which has been boiled. The reaction is now less intense. 



