( 1075 
that these tyrosine-vibrios of the sea can be accumulated in seawater 
with addition of agar as sole source of carbon, ammonium chlorid 
as nitrogen food, and kalium phosphate. In this respect they show 
analogy to the gelase vibrios, which secrete the enzyme gelase by 
which agar is changed into sugar and which are also easily pro- 
dueed in this manner. 
Accumulation of these microbes in seawater with tyrosine as 
source of carbon has not succeeded, as little as with their relatives 
from fresh water, by corresponding experiments. Endeavours to 
accumulate the latter from sewage water with tyrosine as source of 
carbon and nitrogen have produced fluorescents, which thus prove the 
stronger in the competition at such an ‘elective’ cultivation. 
The fresh-water form is fairly common in the sewage water of 
Delft; to obtain it in pure culture the undilute sewage water 
must be poured over a plate of the composition : 
ERD WIBE zen deens. a OD 
DEEOSLE, | Send ERN Na de pre 0.1 
Natrium carbonate é 0.1 
Dikalium phoshate . . . . 0.05 
REED ee a Een chen wed cae? 2 
The superfluous water is allowed to flow off the plate, which is 
cultivated for some days at 30° C. 
It is true that here the tyrosine is at the same time source of 
carbon and of nitrogen, but the method is now a “separative” one, 
as competition is excluded. 
On the second or third day peculiar black spots are seen to appear 
around some colonies and slowly extend over a distance of some 
millimeters *). The black pigment proves able to diffuse only to a 
rather short distance, whilst the enzyme itself remains bound up with 
the bacterial bodies as belonging to the endo-enzymes. That here we 
have. indeed to deal with a true enzyme, is more easily shown in 
the species of the sea than in the fresh-water microbes. To this end 
some material cultivated on broth agar is killed by the vapour of 
chloroform, then transported to a culture plate of the above com- 
position, or to a nutrient liquid of the same preparation, but with 
omission of the agar. At a temperature of 40° C. the black-colouring 
is then rather quickly perceived but, of course, without development 
') As the so generally distributed fluorescent bacteria likewise attack tyrosine 
under production of a light red-brown pigment, there are always found spots of 
that colour on such culture plates, which can, however, by no means be mistaken 
for those of tyrosinase. 
