45 8 DIGESTION AND ABSORPTION 



the duct a small quantity of the solution. Open the tube. Secretion 

 of saliva will again begin, and stimulation of the chorda will again cause 

 an increase in the flow. But after a few minutes the action of the 

 atropine will reassert itself, and the flow will stop. Renewed secretion 

 may be caused by a fresh injection of pilocarpine. 



8. Gastric Juice (a) Preparation of Artificial Gastric Juice. Take 

 a portion of the pig's stomach provided, strip off the mucous membrane 

 (except that of the pyloric end, which is relatively poor in pepsin), cut 

 it into small pieces with scissors, and put it in a bottle with 100 times 

 its weight of 0-4 per cent, hydrochloric acid. Label and put in a bath 

 at 40 C. for three hours, and then in the cold for twelve hours. Then 

 filter. 



(b) Take another portion of the mucous membrane, cut it into pieces, 

 and rub up with clean sand in a mortar. Then put it in a small bottle, 

 cover it with glycerin, label, and set aside for two or three days. The 

 glycerin extracts the pepsin. 



(c) Take five test-tubes, A, B, C, D, E, and in each put a little washed 

 and boiled fibrin or a small cube of coagulated egg-white. To A add a 

 few drops of glycerin extract of pig's stomach, and fill up the test-tube 

 with 0-4 per cent, hydrochloric acid. To B add glycerin extract and 

 distilled water; to C glycerin extract and i per cent, sodium carbonate; 

 to D 0-4 per cent, hydrochloric acid alone; to E glycerin extract which 

 has been boiled, and 0-4 per cent, hydrochloric acid. 



Put up another set of five test-tubes in the same way, except that a 

 few drops of a watery solution of a commercial pepsin are substituted 

 for the glycerin extract. Label the test-tubes A', B 7 , C', D', E'. 



Into another test-tube put a little fibrin (or an egg-white cube), and 

 fill up with the filtered acid extract from (a). Label it F. Place all 

 the test-tubes in a tumbler, and set them in a water-bath at 40 C. 

 Put a piece of a Mett's tube (p. 343) into each of two test-tubes, and 

 add 15 c.c. of 0-4 per cent, hydrochloric acid. To one tube add 5 drops 

 and to the other 10 drops of the same filtered glycerin extract of gastric 

 mucous membrane. Put the tubes in the bath, and when digestion is 

 distinct at the ends of both tubes measure the length of the column 

 digested in each. What is the relation between the two (p. 342) ? 

 The experiment can be repeated with the hydrochloric acid extract of 

 the mucous membrane. 



After a time the fibrin (or egg-white) will have almost completely dis- 

 appeared in A, A', and F, but not in the other test-tubes. Filter the 

 contents of A, A', and F into one dish. 



(d) Test the filtrate for the products of gastric digestion : 



(a) Neutralize a portion carefully with dilute sodium hydrox- 

 ide. A precipitate of acid -albumin may be thrown 

 down. Filter. 



(jS) To a portion of the filtrate from (a) add excess of sodium 

 hydroxide and a drop or two of very dilute copper 

 sulphate. A rose colour indicates the presence of 

 proteoses or peptones. The cupric sulphate must be 

 very cautiously added, because an excess gives a violet 

 colour, and thus obscures the rose reaction. If still 

 mere cupric sulphate be added, blue cupric hydroxide 

 is thrown down, and nothing can be inferred as to the 

 presence or the nature of proteins in the liquid. 



(y) Heat another portion of the filtrate from (a) to 30 C., 

 and add crystals of ammonium sulphate to saturation. 

 A precipitate of proteoses (albumoses) may be ob- 

 tained. Filter off. 



