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which has first been brought to certainty by Mr. HAZEWINKEL, and, 
without my knowing of his experiments, by myself. Woad, as an 
yindoxyl-plant” containing no indigo-glucoside, wants also an enzyme 
to decompose it. The two mentioned ,indican-plants’, on the other 
hand, do contain such an enzyme, which had already in 1893 been 
rendered probable by Mr. VAN LOOKEREN CAMPAGNE with regard 
to Indigofera’). I have prepared this enzyme, albeit in a very 
impure state, in rather great quantity and I hope afterwards to 
describe the experiments made with it. 
The important difference between ,indoxyl-” and „indican- plants” 
becomes particularly clear when comparing the different extraction 
methods. 'Thereof what follows. 
If ,indican-plants” are extracted with water below the tempe- 
rature at which the indigo-enzyme becomes inactive, for instance 
below 40° C. or 50° C. („cold extraction’’), and under careful exclu- 
sion of air, an indoxyl-solution is obtained. If, however, the same 
„indiean-plants’’ are extracted by boiling (,decoction’’), the indigo- 
enzyme will be destroyed, and independently of removal or access of 
air, an indican-solution results, which can be kept perfectly unchanged 
when microbes are excluded, but either by the separately prepared 
indigo-enzyme, or by certain bacteria or yeasts, or also by boiling with 
acids, it can be converted into the constituents indoxyl and sugar. 
I have prepared from it the crude indican in a dry state, by evapor- 
ating to dryness the decoctions of both Zndigofera leptostachya and 
Polygonum tinctorium. The brown matter, thus produced, resembles 
sealing-wax, is very brittle and can quite weil be powdered. 
Woad on the contrary, as an „indoxyl-plant”, both by „cold 
extraction’ and by ,decoction” always gives the same produce 
i. e. an indoxyl-solution. Here, in both cases, the greatest care 
must be taken to exclude the air in order to prevent that the 
indoxyl, which is so easily oxidised, is converted already in the 
leaf itself, for then the iudigo-blue is lost. Besides, access of air in 
a dying wood-leaf gives still in another way cause to loss of indoxyl 
under formation of unknown colourless and brown substances. — 
A sufficient removal of air during the preparation of the extracts 
is easily effected in the following way?) A well closing, wide- 
mouthed stoppered bottle is quite filled up with woad-leaves, hot 
1) Verslag omfrent onderzoekingen over indigo, pag. 12, Samarang 1893. 
2) The technical preparation of indigo from woad is described in Giopert, Traité 
sur le Pastel, Paris 1813, and in De PuyMAURIN, Instruction sur l'art d’extraire 
Indigo du Pastel, Paris 1813. 
