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only an impure indigo can be obtained by means of their action. 
In consequence of the growth of Aérobacter the reaction of plant 
extractions, particularly of the indigo-plants, first becomes feebly acid, 
later feebly alkaline by the formation of free alkali. This is also 
prejudicial to the production of indigo, as in acid solutions the 
indoxyl oxidises very slowly, by which again much indigo-red is 
formed, while at the same time part of the indoxyl gets lost in 
another way. 
Worthy of note is the influence of varions sugars on the indican 
decomposition by Aérobacter. Mr. VAN HasseLT found that already 
Ijs pCt. glucose, as well in liquid cultures as in gelatine experiments, 
prevents decomposition, while much larger quantities, even to 10 pCt. 
of cane-sugar, maltose and lactose have no effect at all and levulose 
but very little. Evidently the very sugar produced by the splitting 
counteracts this splitting, while other sugars have not this effect, 
or in less degree. To this rule mannose makes an exception, as 
indican decomposition is in the same way counteracted by it as by 
glucose. This opposing influence gives consequently only partly and 
not completely the answer to the question after the nature of the 
sugar separated out of the glucoside by bacteria }). 
There are however forms of Aérobacter which, in ferment-experi- 
ments, produce uneaual quantities of carbonic asid und hydrogen 
from glucose and mannose, and by their help it is proved that the 
sugar formed from indican can only be glucose. 
Nitrates, also, have a remarkably opposing influence on the 
production of indigo by Aérobacter. Common saltpetre is active 
already at 1/.) pCt., which is in perfect accordance with the anti- 
fermenting action of this salt in general, on which reposes its use 
in the dairy industry, to prevent one of the most important defects 
of cheese, in Holland called “rijzers”. 
6. Indican-decomposition by the Indigo-enzymes. 
The indigo-enzymes prepared from Indigofera leptostachya, Poly- 
gonum tinctorium, Phajus grandiflorus, aethyl-acetate-yeast (Saccha- 
romyces sphaericus) and emulsine of sweet almonds, have been 
1) Mr. van HasseLT prepared the osazon from the indican-sugar and found, after 
reerystallisation from alcohol, the melting point to be at 195° to 199° C., that is nearly 
the same as tnat of glucosazon, which is 204° to 205° C. But the melting point of 
mannosazon is about as high. 
