Finally it may be remarked that quercite (which is not susceptible of alcohol 

 fermentation) is attacked, when no air is admitted, by fermentation bacteria of the 

 Aerobacter-group, such as A. aerogenes, under production of carbonic, hydrogen, and 

 of organic acids which have not been more exactly examined. 



3. Oxidation of Tyrosine to Melanine by Microspira tyrosinatica. 



It is well known that the enzyme tyrosinase is able to oxidise tyrosine to a 

 jet-black substance, which is formed at the air from dioxyphenyl acetic acid or 

 homogentisinic acid. It is accepted that this substance originates after the formula *) : 



CHuNO 8 + O 3 = C 8 H 8 O4 + NH 3 + CO 2 . 

 Tyrosine Homogentisinic acid 



In the experiments now to be treated I could not find ammonia which, according 

 to the formula should come free, probably because all the nitrogen present in the 

 tyrosine, is used for the growth of the bacteria. 



Hitherto this conversion had only been studied as a consequence of the action 

 of an enzyme occurring in higher plants and also in higher Fungi. Nobody, however, 

 had as yet described tyrosinase-producing bacteria, whose existence will be referred 

 to in the next lines. As they are rather easily cultivated and are able to produce 

 great quantities of the black pigment formed from tyrosine, which is identic with or 

 closely allied to the melanines of the human body, they are of importance for ex- 

 perimental physiology. 



Tyrosine microbes are small vibrios, chiefly occurring in the sea and during the 

 winter months present in the plankton. Fresh water is not however quite devoid of 

 them and without much trouble they may be isolated from sewage water. The 

 forms living in the sea produce, at least as regards the stronger varieties, besides 

 tyrosinase, also tyrosine, and as this takes place from peptone they are to be recog- 

 nised by the black stains which their colonies produce on broth-agar plates which, 

 as we have to deal here with inhabitants of the sea, should contain 3 proc. common 

 salt. It is remarkable that these tyrosine-vibrios of the sea can be accumulated in 

 seawater with addition of agar as sole source of carbon, ammonium chlorid as ni- 

 trogen 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 produced 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: 



*) Abderhalden, Physiolog. Chemie. 2te Aufl. p. 367, 1909. 



