CHAPTER IV 



OSMOSIS AND DIGESTION 



Materials : Four thistle tubes, four wide-mouthed bottles ; honey, 

 molasses, or a thick solution of grape sugar ; starch (arrowroot if 

 possible), diastase ; white of egg, peptone ; iodine, Fehling's solution, 

 nitric acid. Procure the intestines of calf or beef, wash them thor- 

 oughly inside and out, and inflate them by the aid of a glass tube. 

 Tie at intervals of two or three feet, and allow this animal mem- 

 brane to dry. Cut off pieces about two inches long, and slit open 

 each of the pieces thus obtained. Membrane 

 prepared in this way may be kept in closed 

 bottles for years. If desired, the pieces of 

 membrane may be used at once without dry- 

 ing. Sausage coverings that have been pre- 

 served in salt may be thoroughly washed, 

 dried, and used. 



Thistle tube No. L Hold one of the thistle 

 tubes upright, closing the smaller end by press- 

 ing on it with the thumb. Into the larger 

 end pour the honey, molasses, or grape sugar 

 solution, which has been sufficiently warmed to 

 pour easily. Half fill the tube and nearly fill 

 the bulb. Moisten one of the pieces of intestine 

 and tie it tightly over the bulb of the thistle 

 tube so that none of the liquid can escape. 

 Wash off any of the liquid from the outside of 

 the membrane, then dry it with a blotter, and 

 hold the thistle tube bulb down for several minutes to make sure 

 that the grape sugar solution does not leak out. Now stand the 



32 



FIG. 8. Apparatus 

 for thistle tube 

 No. 1 in osmosis 

 experiment. 



