244 



PRACTICAL PHYSIOLOGY 



hydrochloric acid and some other body (acetic acid, or an alcohol 

 according to the method of preparation) called hsemin can be 

 obtained from haemoglobin, which crystallises in chocolate-brown 

 rhombic plates. This forms one of the chemical tests for blood. 



EXPERIMENT XI. Preparation of Hcemin Crystals. Place a drop 

 of blood upon a glass slide and warm until dry. Scrape loose the 

 brown residue, add a little glacial acetic acid, cover with a cover 



FIG. 178. Hsemin. x 1,500. 



glass and warm very gently until bubbles form. Remove from 

 flame. If necessary add a little more acid, and warm again till 

 bubbles form. Repeat the operation two or three times. When 

 cold examine with microscope for the dark-brown hsemin crystals 

 (Fig. 178). 



There is sufficient chloride in blood to give the test without the 

 addition of any sodium chloride. If, however, an old blood stain 

 be used, it is necessary to add a small crystal of sodium chloride 

 in case the chloride of the blood has been washed out. Bromide 



