230 



COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



Precipitate. On 

 small portions try 

 the glyoxylic reac- 

 tion for tryptophane 

 and Millon's reac- 

 tion for tyrosine. 

 The former is in- 

 tense : the latter 

 negative or feeble. 



Filtrate. On portions apply the same 

 two reactions. Millon's is intense : the 

 glyoxylic is negative or feeble. To the 

 remainder add 40 per cent, soda drop by 

 drop until the reaction is nearly neutral. 

 Filter. 



Precipitate. Ap- 

 ply Millon's test. A 

 fairly strong reac- 

 tion is obtained. 



Filtrate. Apply 

 Millon's test. A 

 negative or feeble 

 reaction is obtained. 



Tryptophane is precipitated by the mercuric reagent, even in 

 the presence of 7 per cent, sulphuric acid. Tyrosine is not pre- 

 cipitated in this strength of acid, but is precipitated in a solution 

 that is only faintly acid. 



It is not easy to obtain crystals of tyrosine or leucine by direct 

 evaporation of the original solution. This is apparently due to the 

 presence of purine bases and other compounds. If these be first 

 removed by precipitation with phosphotungstic acid in 3 per cent, 

 sulphuric acid solution (the fluid also being acidified to this extent) 

 and the two acids be removed by baryta, the filtrate gives crystals 

 of tyrosine and leucine on evaporation. 



L. Oxidases, Peroxidases, and Tyrosinase. 



The mechanisms concerned in the oxidations in the 

 body of such relatively stable substances as fats and 

 carbohydrates are by no means fully understood. It is 

 generally believed that it is due to the action of enzymes, 

 which are either very unstable or are only active when 

 associated with living protoplasm. This would account 

 for the fact that the ingestion of protoplasmic poisons, such 

 as quinine, has a distinct inhibitor} 7 " influence on various 

 oxidative processes in the body. There is an increasing 

 amount of evidence to indicate that the sulphur con- 



