432 A MANUAL OF PHYSIOLOGY 



(/) 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, solution of potassium 

 ferrocyanide in 0-5 per 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 glycerin 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. Sections of spleen may also be examined 

 for this reaction. 



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. 396). 



9. Absorption of Fat. (a) 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 glycerin and examine under the microscope. 

 To preserve the specimens take off the glycerin with blotting-paper 

 and mount in Farrant's medium, which is a preservative glycerin 

 mixture. 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). 

 (See Fig. 156, p. 413.) 



(b) Feed a cat with 30 grammes of butter stained a deep red with 

 the dye Sudan III. After five hours anaesthetize the animal with 

 ether, insert a cannula in the carotid artery, and obtain a sample 

 of blood. Defibrinate the blood, and separate the serum by the 

 centrifuge. If digestion and absorption of the fat have proceeded 

 normally, the serum will contain numerous fat droplets, and will be 

 tinged pink by the dye, which can be dissolved out of it by shaking 

 up with ether. On opening the abdomen it will be seen that the 

 mucous membrane of the small intestine, as far down as the fat has 

 reached, is stained pink, and that the lacteals in the mesentery are also 

 pink. Observe whether any of the pigment has passed into the urine. 



10.* Time required for Digestion and Absorption of Various Food 

 Substances. Feed three dogs, A, B, and C, which have previously 

 fasted for twenty-four hours, with a meal containing starch (proved 

 to be free from sugar), lard, and meat. 



(i) After fifteen minutes inject subcutaneously into A 2 c.c. of a 

 o-i per cent, solution of apomorphine. Note the time which elapses 

 before the animal vomits. Collect the vomit. 



* Experiments 10 and n are conveniently done in a class by assigning 

 each of the three animals to a separate set of students. The contents of 

 the stomach and intestine are divided into three portions, so that each 

 set has a sample from each dog. 



