ENZYMES AND OTHER FERMENTS DIGESTION. 139 



necessary for the change being taken from the air. The ac- 

 tion of this enzyme or oxidase may be shown in other ways, 

 especially by the use of hydroquinol and pyrogallol, which 

 substances yield very dark solutions when oxidized. It is 

 simply necessary to make an aqueous extract of certain veg- 

 etables and fruits and add this to the aqueous solution of the 

 hydroquinol to produce the dark color. Here the enzyme 

 appears to be active enough to carry oxygen to the hydro- 

 quinol. 



Laccase and Tyrosinase. These are the names which 

 have been given to two of these oxidases. The first was orig- 

 inally found in the sap of the Japanese lac tree, which when 

 expressed and exposed to the air darkens and produces the 

 well-known lacquer. The same laccase is said to be one of 

 the agents which brings about the darkening in many other 

 saps and juices. Tyrosinase acts on the phenol derivative 

 tyrosine which is found in traces in many vegetables and 

 causes its oxidation. 



It is held by many physiologists that similar substances are 

 found in the animal body and are there responsible for the 

 oxidations going on continuously. These assumed enzymes 

 must be found especially^ the tissues where the food elements 

 are being rapidly broken down by the oxygen carried along in 

 the blood stream. Thus far, however, no satisfactory proof 

 has been advanced to show the existence of such oxidizing 

 enzymes. The various extracts made from certain organs and 

 investigated from this standpoint have been found to be either 

 inactive or to work in a limited direction only. Extracts from 

 the liver and spleen have been found able to convert xanthine 

 and hypoxanthine into uric acid, but this fact, important as it 

 may be, is far from throwing any light on the oxidation of 

 sugar to form water and carbon dioxide. Of these animal 

 oxidases it may be said in general that our knowledge is not 

 exact enough to justify a very long discussion in an elemen- 

 tary manual. 



