380 A MANUAL OF PHYSIOLOGY 



present in the gastric mucous membrane. The rennet ferment is 

 active in an acid or neutral, bjit inactive in an alkaline, medium. 



(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. 378). 



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

 lactic acid by UefTelmann's test, and for hydrochloric acid by Guns 

 burg's reagent. 



Ueffelmann's Test for Lactic Acid. The reagent is a dilute solu- 

 tion 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 hydrochloric acid. 



Giinsburg's Keagent 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 proteids 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 glycerine extract in the same way as in 

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

 aside for a day or two. 



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

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

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

 glycerine extract and distilled water; to C glycerine extract and 

 excess of 0-05 per cent, hydrochloric acid ; to D i per cent, sodium 

 carbonate alone ; to E i per cent, sodium carbonate in which a few 

 drops of glycerine extract of pancreas have been previously boiled; to 

 F glycerine extract and excess of 0*2 per cent, hydrochloric acid.* 



Set up six test-tubes, A', B', C', D', E', F', in the same way, but | 

 substitute a few drops of a solution of commercial pancreatin for the > 

 glycerine extract. Put all the test-tubes in a tumbler, and place in 

 a bath at 40 C. The fibrin will be gradually eaten away in A and A' / 

 by the action of the trypsin, but will not swell up or become clear . 

 before disappearing, as it does in dilute hydrochloric acid with 

 glycerine extract of stomach. Filter the contents of these test-tubes. 



* With hydrochloric acid of different strengths the rapidity of digestion 

 of boiled fibrin by glycerine extract of dog's pancreas (i volume of extract 

 to 25 of acid) was found about the same for 0^3 and 0^17 per cent, acid ; 

 much less for O'o8 per cent., while in 0*04 per cent, acid there was prac- 

 tically no digestion at all. In 0*4 per cent, acid digestion took place 

 more rapidly than in 0*08 per cent., but much less rapidly than in o'i7 

 per cent. In acid of all strengths digestion was markedly slower than in 

 i per cent, sodium carbonate. 



