937 
In order to ascertain how in this respect the tyrosinase of the 
higher plants behaves, I took strong tyrosinase preparations derived 
from the potato, the beetroot and latex of Muphorbia Lathyris*) 
which quickly colour tyrosin solutions deep black, and made them 
act on homogentisinic acid salts. The latex of Huphorbia Lathyris 
is extremely fit for these experiments as it can always be made to 
drip from the living plant, which supports our winters very well in the 
garden. A single drop on an agar-tyrosin plate at from 30° to 50° C. 
forms deep black melanin spots after a few hours already. But homo- 
gentisinie acid can also be oxidised with great velocity. For this 
experiment I used an agarplate of this composition: water, 2°/, agar, 
0,5°/, natrium ,homogentisinate, 0,02°/, NH,CI and 0.02°/, K,HPO,,. 
On this plate drops of the latex were put and besides streaks were 
made of Actinomyces and the symbiotic bacterium. After some hours, 
at 30° C., dark brownish black fields appeared, evidently more 
readily formed than the black fields from the tyrosin. 
After about 24 hours Actinomyces also began to grow but no 
pigment at all appeared, as was to be expected. The symbiotic 
bacterium did not develop under these conditions. But some broth 
being added to a like medium the bacterium could grow and oxidised 
the homogentisinic salt. to melanin. So it is certain that also 
the tyrosinase of Huphorbia Lathyris must be a mixture of two 
oxidising enzymes; one of these, which may preserve the name of 
tyrosinase, produces hemogentisinie acid from tyrosin, the other, 
“homogentisinase”’, forms melanin from the acid, and corresponds with 
the oxidase of the symbiotic bacterium. This enzyme requires no 
special name as “homogentinase” and “‘laccase” are probably identic. 
Although the “two enzymes theory” of the tyrosinase may be 
considered as confirmed by what precedes, still it should be called 
to mind that, when a method of experimenting is used somewhat 
deviating from the described the above result with Kuphorbia Latyris 
is not obtained. Such is, namely, the case when the milky juice of 
the plant is put on agarplates with homogentisinic acid salt, with 
addition of oroth for the baeteria. Then the surprising fact occurs 
that the bacterium is active but the latex is not. Whereon this 
difference reposes is not clear. 
Finally it may be mentioned that the existence of two enzymes 
in the tyrosinase of the beetroot was already made probable by 
P.C. van per Work (Recherches au sujet de certains, processes enzy ma- 
tiques chez Beta vulgaris, Nimegue 1912). 
r 1) The latex of Euphorbia palustris, E. Peplus, E. helioscopia, E Mysinitis, 
contain no tyrosinase 
