464 DIGESTION AND ABSORPTION 



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 mem- 

 brane of the small intestine, and steep them in \ per cent, solution 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 maae with a freezing microtome after 

 embedding in gum. No process must be used by which the fat would 

 be dissolved out (Schafer). (See Fig. 172, p. 441.) 



(6) 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. 



14.* 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. 



(1) 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. 



(a) Examine a little of it under the microscope, and make out fat 

 globules, muscular fibres and starch granules. The latter can be recog- 

 nized by their being coloured blue by a drop or two of iodine solution. 



(b) Filter the chyme, mixing it, if necessary, with a little water, and 

 test it as in 8 (d) (p. 458) for the products of digestion of proteins. In 

 addition, test for starch, dextrin, and reducing sugar. 



(2) One and a quarter hours after the meal inject apomorphine into 

 dog B, and proceed as in (i). 



(3) Two and a half hours after the meal inject apomorphine into 

 dog C, and proceed as in (i). Compare the results from the three 

 specimens of chyme. 



15.* Quantity of Cane-Sugar inverted and absorbed in a Given Time. 

 Take three dogs, A, B, and C, which have fasted for twenty-four hours. 

 The animals should be about the same size. Feed A and B with 

 100 c.c. of a standard solution of cane-sugar (about a 20 per cent, solu- 

 tion), or as much more as they will take. If the dogs have been kept 

 without water for a day they will more readily take the sugar solution. 

 Or it may be given through a tube passed into the stomach, and in 

 this case a larger quantity of sugar can be given. A gag consisting of 

 a piece of wood with a hole in the middle of it, through which the tube 

 is passed, must first be secured in the dog's mouth. Feed C with 



* Experiments 14 and 15 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. 



