CELL-CONTENTS AND CELL-WALLS. 49 



57. Preparation of Trypsin. There are various commercial 

 preparations which contain trypsin, e.y. Benger's "liquor pancrea- 

 ticus " (which often contains a sediment of tyrosin), the " Holadin " 

 of Fairchild Bros, (a very active preparation containing also lipase 

 and diastase). The vegetable trypsin, papain, can also be obtained ; 

 it contains only trypsin. 



To make a glycerine extract of pancreas, which will serve also 

 for experiments on the hydrolysis of starch ( 74) and that of oils 

 ( 86), mince up a fresh ox or pig pancreas ("sweetbread") in the 

 same way as directed for the gastric extract ( 54). 



58. Experiments with Trypsin. Repeat the experiments 

 directed for pepsin ( 55), but instead of acid use 1 per cent, sodium 

 bicarbonate solution. To prevent putrefaction, add some anti- 

 septic such as thymol, or toluene, or chloroform water (5 c.c. of 

 chloroform shaken with a litre of water). 



Label thiee test-tubes A, B, C. Half fill each with 1 per cent, 

 sodium carbonate solution, and add some hard-boiled egg white, 

 with a few drops of the antiseptic. Boil B ; make G acid with 

 dilute hydrochloric acid. Plug the three tubes with cotton-wool, 

 and place them in a bath at 40 for an hour. In A the liquid 

 becomes more or less clear, the albumin being digested ; in B and 

 C there is no change. 



Filter the liquid in A , neutralise the filtrate with dilute acid ; 

 alkali albumin is precipitated filter this precipitate off and test 

 the filtrate for peptones. 



Filter B and C, and neutralise B with acid and C with sodium 

 carbonate ; no precipitate is formed. Test for peptones none are 

 present. In B the trypsin has been destroyed by the boiling, in 

 C its action is prevented by the presence of the acid. 



59. Products of Tryptic Digestion. Make a tryplic diges- 

 tion on a larger scale, so as to study the products more fully. Two- 

 thirds fill a large flask (1 or 2 litres capacity) with 1 per cent, 

 sodium carbonate solution ; add the chopped white of a hard boiled 

 egg ; then some trypsin solution or pancreas extract ; and finally 

 some antiseptic this is essential since tryptic digestion is otherwise 

 accompanied by active putrefaction or bacterial decomposition, by 

 which evil-smelling products (indol, skatol, sulphuretted hydrogen, 

 etc.) are formed. After two or three days, filter t!.e liquid. 



(a) The sediment or precipitate in the liquid contains tyrosin. 

 After filtering, dissolve a portion of the precipitate in dilute hydro- 

 chloric acid, end test with Millon's reagent the solution becomes 

 red. 



(b) Acidify about 5 c.c. of the filtrate with acetic acid, then add 

 bromine water drop by drop a reddish colour appears, which 

 gradually deepens, then disappears as more bromine water is added. 

 When the colour is no longer deepened on adding bromine water 



P. B. 4 



