ANIMAL OXIDATIONS. 447 



the ferments belonging to this organ are capable of converting aldehydes 

 (e.g., salicylic aldehyde) into the corresponding acid, but they are inca- 

 pable of effecting the indophenol synthesis. Jacoby l was unable to effect 

 the oxidation of such compounds as acetic acid, stearic acid, etc., by 

 means of the ferment which changes salicylic aldehyde into salicylic acid. 

 Again, ferments are known which will turn tincture of guaiacum blue, but 

 have no action upon salicylic aldehyde. 2 



Particularly in the vegetable kingdom we meet with these ferments 

 possessing a quite specific oxidation power, which are designated with 

 particular names according to the work that they perform. In the 

 sap of plants we often find the so-called tyrosinase? i.e., a ferment 

 which transforms tyrosine into colored products. The same, or at 

 least a very similar ferment, also occurs in animal organisms. Thus 

 the stomach juices of starved meal-worms act upon tyrosine. 4 A 

 similar action explains an old observation. As is well known, the blood 

 of insects is nearly colorless, but becomes dark as soon as it leaves the 

 body. Von Fiirth and Schneider 5 have found that this so-called melanosis 

 is the result of the action of an oxidizing ferment. They proved this in 

 the following manner: They obtained, by piercing the pupaB of DeilephUia 

 elepenor and euphorbia, a greenish-colored liquid, from which they obtained 

 a precipitate upon the addition of ammonium sulphate. This precipitate, 

 on being dissolved in . 05 per cent soda solution, and added to a solution 

 of tyrosine, soon caused a violet coloration, which gradually turned black. 

 Eventually dark flocks of a precipitate were thrown down. The tyro- 

 sinase thus obtained acts upon other aromatic compounds, containing 

 hydroxyl groups, such as catechol, chinol, etc. In the insect blood itself, 

 tyrosine is not present, but a chromogen, which is evidently closely related 

 to it. It may be assumed safely, that tyrosinase is very abundant in 

 nature, and undoubtedly plays an important part in the formation of pig- 

 ments. In the blood of the river-crab and in the ink-glands of the cepha- 

 lopoda a tyrosinase is found. 



Tyrosinase is much more widely distributed in the vegetable kingdom 

 in which it was discovered, Bertrand 6 has found besides the tyrosinase 

 a second ferment, laccase, which acts upon only quinol and pyrogallol. 



Closely related to these ferments is the glucolytic ferment, which we 

 have already discussed, 7 but whose existence, however, has not been posi- 



1 Virchow's Arch. 157, 235 (1899). 



2 Abelous et Biarnes: Compt. rend. soc. biol. 49, 175, 285, 493, 559, 596; 50, 495. 



3 E Bourquelot and G. Bertrand: J. pharm. chim. (6) 3, 177 (1896); Bull. soc. mycol. 

 France, 1896, 18 and 27. 



* W. Biedermann: Pfliiger's Arch. 72, 105 (1898). 

 * Hofmeister's Beitrage: 1, 229 (1901). 



Compt. rend. 122, 1132, 1215 (1895); 123, 463 (1896). 

 ' See Lecture IV, p. 73, and V, p. 87. 



