ANTI-FERMENT REACTION 349 



Since then, anti-enzymes have been discovered for Hpase, 

 amylase, pepsin, papain and urease. Anti-trypsin and anti- 

 rennet occur normally in the blood, and, according to Wein- 

 land,* anti-pepsin and anti-trypsin occur in the mucous 

 membranes of the stomach and intestine respectively. 



In this connexion the work of Czapek f on the anti-ferment 

 reaction in tropistic movements of plants is of particular inter- 

 est. It is impossible here to give a complete account of the 

 investigations referred to, but the following facts will give 

 some idea of the phenomena under discussion. 



1. It was found that the roots of Vicia Faba when sub- 

 jected to the stimulus of gravity always reduced silver more 

 effectively than unstimulated roots. The mode of testing is 

 as follows. The roots, stimulated or otherwise, are cut into 

 longitudinal slices and boiled in an ammoniacal solution of 

 silver nitrate ; the darkness assumed by the preparations is an 

 indication of the amount of silver reduced. 



2. If the roots of the lupin, for example, be anaesthetized, 

 a deposition of tyrosine, in the shape of spherical crystals, 

 takes place ; but, strangely enough, not in the root-tip, nor in 

 the youngest parts of the growing regions where the maxi- 

 mum reduction of silver takes place. 



The question naturally arises, is there any connexion be- 

 tween the reduction of silver and the production of tyrosine? 

 As a matter of fact there is, for it was observed that in roots 

 containing much crystalline tyrosine, although at first the 

 tyrosine-containing cells did not reduce silver, they did so 

 eventually, the silver reducing properties becoming more and 

 more marked as the tyrosine disappeared, so that eventually 

 a very strong reduction obtained. 



By these and similar observations it was shown that the 

 tyrosine disappears by means of a ferment, tyrosinase, and 

 that one of its products is the substance which reduces the 

 silver. Tyrosinase appears to be widely distributed in plants, 

 e.g. it has been identified in Russula, in the tubers of the 

 Dahlia, in the beetroot, as well as in root-tips. The product 

 of the decomposition of tyrosine referred to above is homo- 



*Weinland: " Zeit. f. Biol.," 1903,44, 45. 

 + Czapek: "Ann. Bot.," 1905, 19, 75. 



