932 
Microbiology. — “On the composition of tyrosinase from two 
enzymes’. By Professor Dr. M. W. BeIJERINCK. 
(Communicated in the meeting of December 28, 1912) 
The product of the action of tyrosinase on tyrosin is commonly 
called melanin, whose colour may be jet black, but takes ail shades 
between light brown, pure red, brownish red, sepia and black in expe- 
rimental conditions. These pigments are of uncommon stability and 
resist even heating with strong alkalies and sulfuric acid, whereby the 
black runs somewhat into brown but in chief remains unchanged. 
Even when boiled with nitric acid the melanin remains almost un- 
changed. It is accepted that the pigment of the hair and hide of 
higher animals is associated with these substances and is derived from 
tyrosin. 
Melanin formation by symbiose of an Actinomyces with a bacterium. 
On a culture plate of the composition : distilled water, 2°/, agar, 
0.1 °/, tyrosin (dissolved in a few drops natriumcarbonate) and 
0.02 °/, K,HPO,, on which some centigrams garden soil are sown and 
which is kept at 380° C., hundreds or thousands of little sods of Actino- 
myces (Streptothriz) will develop after two or three days. The tyrosin 
serves at the same time as source of carbon and of nitrogen. But 
the agar itself also is attacked by these microbes, although with 
difficulty, and used as food. This is not surprising as many Actino- 
myces-species can even live on cellulose as source of carbon. 
The common bacteria of the soil develop not or hardly on the 
tyrosin plate and cannot in the given circumstances compete with 
the slowly growing Actinomyces as they do on better media, e.g. on 
broth agar, where Actinomyces never occurs when bacteria are 
present. 
As the delicate threads of this genus enter deep into the agar, the 
plates may be freed by washing from the bacterial colonies and the 
adhering soil; then the Actinomyces sods can be easily counted. In 
humus and humus containing soil their number is amazing. When 
they can freely multiply on plates which are poor in food their growth 
is unlimited and they produce sods of great extension, even of one 
or more decimeters in surface, commonly producing very fine 
mycelial-rings, which by turns bear spores or not. These rings are 
independent of light and suggest a periodicity in the nutrition not 
yet fully explained. 
In somewhat extensive culture experiments, similar to the above, 
it may with certainty be expected that at some places brownish 
