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protoplasm is killed or hurt, but in which the enzyme remains active. 
During the dying the protoplasm becomes permeable, indican and 
enzyme are mixed up, and indoxyl-formation is the result. But in 
the same cells there occurs, in consequence of the slowly succeeding 
death, an alkaline reaction, by which the indoxyl soon oxidises to 
indigo-blue, which therefore precipitates in these cells alone, and 
not in the quickly killed nor in the living cells. Put into ammoniac- 
vapour the living, as well as the dead part of the Polygonum-leaf 
remain uncoloured, in opposition to the woad-leaf, this, after the 
preceding, requires no further elucidation. 
Of course, these phenomena would find a somewhat simpler explan- 
ation if they could be brought back to the action of an oxidase, 
present from the beginning. But an oxidase, producing indigo from 
indoxyl is, as said, not to be found. 
To conclude I wish to observe, that some other phenomena, which 
are attributed to the effect of a ,wound-irritation”, for instance, the 
formation of starch and of red pigment, as also the development of 
warmth in hurt parts of plants, possibly repose also on alkali- 
formation in or near the damaged cells. 
Physics. — Communication NO. 51 from the Physical Laboratory 
at Leiden by Prof. H. KAMERLINGH Onnes: “Methods and 
apparatus used in the cryogenic laboratory”. 1. 
1. Last year the completion of the safety-arrangements, thought 
desirable for the cryogenic laboratory by the Privy Council, in accor- 
dance with the Report of the committee appointed by the Academy, 
enabled us again to take up the work. I intend now to publish, 
whenever the completion or the progress of researches allow, something 
about the methods and apparatus used in working at low tempe- 
ratures and with liquefied gases. 
In this way the short survey (Comm. N°. 14) of the arrangement 
of the cascade formed by the methylchloride-, ethylene- and oxygen- 
cycles will be continued or elaborated. 
2. Cryostat (boiling-glass and boiling-case) for measurements 
with liquefied gases (especially with liquid oxygen). 
In the above mentioned communication a method was described 
(§ 8) for using liquid gases in measurements. A sketch, shown on 
plate I of Communication N°. 27+), may serve in some way to 
‘) Verslag der Vergad. Kon. Akad. 96/97. pg. 37. Comm. Leyden, N°, 27. 
