382 A MANUAL OF PHYSIOLOGY 



(c} Cholesterin (Fig. 115). Preparation. Extract a powdered 

 gallstone (preferably a white one) with hot alcohol and ether in a 

 test-tube. Heat the test-tube in warm water, not in the free flame. 

 Put a drop of the extract on a slide. Flat crystals of cholesterin, 

 often chipped at the corners, separate out. Carefully allow a drop 

 of strong sulphuric acid and a drop of dilute iodine to run under the 

 cover-glass. A play of colours violet, blue, green, red is seen. 

 Evaporate a drop of the solution of choles- 

 terin in a small porcelain capsule, add a drop 

 of strong nitric acid, and heat gently over a 

 flame. A yellow stain is left, which becomes 

 red when a drop of ammonia is poured on it 

 while it is still warm. 



(f) To demonstrate the Presence of Iron in 

 the Liver Cells. Steep sections of liver in a 

 solution of potassium ferrocyanide, and then 

 in dilute hydrochloric acid. Or a 1*5 per cent. 

 FIG. 115. CHOLKS- solution of potassium ferrocyanide in 0^5 per 

 TERIN CRYSTALS. cent, hydrochloric acid may be used. (The 

 iron may previously be fixed in the tissue by hardening it in a 

 mixture of alcohol and ammonium sulphide.) The sections become 

 bluish from the formation of prussian blue. A fine-pointed glass rod 

 or a platinum lifter should be used in manipulating them. A steel 

 needle cannot be employed. Mount in glycerine or Farrant's solu- 

 tion, or (after dehydrating with alcohol and clearing in xylol) in 

 xylol-balsam. Blue granules may be seen under the microscope in 

 some of the hepatic cells. 



(g) To some starch mucilage, shown to be free from sugar, add a 

 little bile, and place in a bath at 40. After a time test for reducing 

 sugar. Report the result. 



8. Microscopical Examination of Faeces. Examine under the 

 microscope the slides provided. Draw, and as far as possible deter- 

 mine the nature of, the objects seen (p. 358). 



9. Absorption of Fat. Feed a rat or frog with fatty food ; kill 

 the rat in three or four hours, the frog in two or three days. Imme- 

 diately after killing the rat open the abdomen, carefully draw out a 

 loop of intestine, and look through the thin mesentery. The white 

 lacteals will probably be seen ramifying in the mesentery. They 

 appear white on account of the presence of globules of fat in the 

 chyle with which they are filled. Strip off tiny pieces of the mucous 

 membrane of the small intestine, and steep them in \ per cent, solu- 

 tion of osmic acid for forty-eight hours. Then tease fragments of the 

 mucous membrane in glycerine, take off the glycerine with blotting- 

 paper, mount in Farrant, and examine under the microscope. Other 

 portions of the mucous membrane may be hardened for a fortnight 

 in a mixture of 2 parts of Miiller's fluid and i part of a i per cent, 

 solution of osmic acid. Sections are then made with a freezing 

 microtome after embedding in gum. No process must be used by 

 which the fat would be dissolved out (Schafer). 



