426 A MANUAL OF PHYSIOLOGY 



effect of stimulation of the chorda. See whether the sympathetic 

 is also inactive, and report the result. 



(2) Now empty the cannula in the submaxillary duct by means of 

 a feather, and fill it with a 2 per cent, solution of pilocarpine nitrate 

 by means of a fine pipette. Fill also the short rubber tube attached 

 to the cannula, and close it again. Compress the tube, and so force 

 into 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. 



4. 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 sub- 

 stituted for the glycerin extract. Label the test-tubes A', B', 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. 422) 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. 317) ? 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 

 disappeared 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 

 hydroxide. A precipitate of acid-albumin may be 

 thrown down. Filter. 



(/3) 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 



