228 COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



and the sulphuric acid removed by the addition of a hot saturated 

 solution of baryta, which should be added until the reaction is faintly 

 alkaline to litmus paper. The barium sulphate is filtered off by means 

 of a Buchner funnel. The filtrate is cautiously treated with dilute 

 sulphuric acid until no further precipitate is obtained and filtered 

 again. The nitrate is made faintly alkaline to litmus, and diluted, 

 if necessary, to make a total volume of about 4 litres. 0-5 gram, per 

 cent, of sodium chloride is added, and the reaction adjusted to 

 about P H = 7-35. It is then distributed into flasks and sterilised in 

 the autoclave. One flask, labelled C, is inoculated with a culture 

 of B. coli and labelled C. Another flask is treated with o-i gram. 

 per cent, of pure tryptophane, heated for ten minutes on a boiling 

 water bath, cooled, inoculated with B. coli, and labelled D. Another 

 flask, labelled E, is taken as a control. The three flasks are incu- 

 bated for 2 to 5 days at 38 to 40 C. 



(i.) On portions of the three fluids perform tests for indol by 

 Exs. 269 and 270. They are only obtained in D. 



(ii.) Apply the glyoxylic test or the bromine test (Ex. 88, 

 A and B) for tryptophane to E. Neither are obtained, owing to the 

 destruction of tryptophane during the acid hydrolysis of the casein. 

 The experiment proves that tryptophane is the only amino-acid 

 which yields indol on bacterial decomposition. 



K. Autolysis. 



When an organ is removed from the body and incubated 

 for several days at 38 C. in the presence of an antiseptic 

 such as toluol, it is found that a certain amount of the 

 tissue proteins have been hydrolysed to amino-acids. This 

 disintegration of the tissues is known as "autolysis." It 

 is due to the action of certain proteolytic enzymes which 

 seem to be present in nearly all tissues, and which are 

 sometimes known as "tissue erepsins." But it must be 

 noted that intestinal erepsin does not act on the native 

 proteins, but only on proteoses, peptones and polypeptides. 

 There must be an essential difference between the two 

 enzymes. 



