428 A MANUAL OF PHYSIOLOGY 



cannula, and cover the animal with a cloth. The following experi- 

 ments may now be performed. Expose both vagi in the neck. 

 Connect two pairs of electrodes with the secondary coil of an in- 

 ductorium arranged for single shocks. By means of a key in the 

 primary stimulate the nerves with slow rhythmical induction shocks 

 at the rate of about one a second. Continue the stimulation for 

 fifteen minutes, collect any juice that may have been secreted, and 

 apply the tests in (3). If secretion is slow, a little distilled water 

 may be put into the stomach, and the vagus stimulation repeated. 

 Mechanical stimulation of the mucous membrane with a feather 

 causes no secretion of acid gastric juice, but may cause a secretion 

 of alkaline mucus. 



(3) (a) Test the reaction to litmus of the chyme obtained in (i), 

 and of the pure juice obtained in (2). 



(b) Test their proteolytic powers by putting in a bath at 40 C. 

 for two hours two test-tubes containing respectively filtered chyme 

 and fibrin, and gastric juice and fibrin. The fibrin will be digested 

 in both. Estimate the proteolytic power quantitatively by Mett's 

 tubes (p. 422). 



(c) Add a few drops of the chyme and gastric juice to milk in two 

 test-tubes, and place them in a bath at 40 C. Repeat (c) after 

 neutralizing the liquids. 



(d) Examine a drop of the unfiltered chyme under the microscope. 

 Partially digested fragments of the food will be seen muscular 

 fibres, or fat cells. Filter, and proceed as in 4 (d) (p. 426). 



(4) Test the filtrate from the chyme and the gastric juice for lactic 

 acid by Uffelmann's test or Hopkins's test (p. 716), and for hydro- 

 chloric acid by Giinzburg's reagent. 



Uffelmann's Test for Lactic Acid. The reagent is a dilute solution 

 of carbolic acid to which dilute ferric chloride has been added till 

 the colour is bluish (say a drop of a i per cent, ferric chloride solution 

 to 5 c.c. of a i per cent, carbolic acid solution). The blue colour of 

 the mixture is turned yellow by lactic acid, but not by dilute hydro- 

 chloric acid. Since Uffelmann's test is given also by phosphates, 

 alcohol, and sugar, which may sometimes be present in the stomach 

 contents, it is best to shake the gastric contents with ether, dissolve 

 the ethereal extract in water, and then make the test on the watery 

 solution. 



Giinzburg's Reagent for Free Hydrochloric Acid in Gastric Juice 

 is made by dissolving 2 parts of phloroglucinol and i part of vanillin 

 in 30 parts by weight of absolute alcohol. A few drops of the reagent 

 are added to a few drops of the filtered gastric juice in a small 

 porcelain capsule, and the whole evaporated to dryness over a small 

 bunsen flame. If free hydrochloric acid is present, a carmine-red 

 residue is left. If all the hydrochloric acid is united to proteins in the 

 stomach contents, the reaction does not succeed. It is also hindered 

 by the presence of leucin. 



6. Pancreatic Juice. (a) Take a piece of the pancreas of an ox 

 or dog which has been kept twenty-four hours at the temperature of 

 the laboratory, and make a glycerin extract in the same way as in 

 the case of the pig's stomach in 4 (b). Put in a small bottle, and 

 set aside for a day or two. 



(6) Put a little boiled fibrin into each of six test-tubes, A, B, C, 

 D, E, F. To A add a few drops of glycerin extract of pancreas, 

 and fill up with a i per cent, sodium carbonate solution ; to B add 

 glycerin extract and distilled water ; to C glycerin extract and 



