184 



PRACTICAL PHYSIOLOGY 



place them on a microscopic slide and break them up with a glass rod, 

 and examine under the microscope, or, better, dissolve some in absolute 

 alcohol, .place a drop of this on a slide, and allow it to evaporate. 

 The crystals are colourless, glancing rhombic plates having usually a 

 square piece removed from one corner (Fig. 141). 



PIG. 141. Crystals of cholesterin magnified 300 diameters. 



EXPERIMENT IX. Place a drop of 20 per cent, sulphuric acid on 

 the crystals and notice that the edges gradually become red. 



EXPERIMENT X. To another specimen add some iodine solution 

 and then a drop of concentrated sulphuric acid a play of red, blue, 

 and green colours results. 



Although cholesterin is not a fat, it is studied with this group 

 because it possesses the same solubilities, and is, therefore, sometimes 

 present in ethereal extracts. 



