

1905.| Stlver Reaction in Anvmal and Vegetable Tissues. 227 
For this purpose the process of purification was modified slightly, the 
gelatin precipitated from the warm solutions was separated by filtration in a 
hot funnel, the filtrate cooled down to 5° C., with the consequent crystallisation 
of the greater part of the sodium sulphate. The mother liquor was then 
concentrated by evaporation, carefully filtered, and on cooling again another 
quantity of crystal sodium sulphate formed.* The mother liquor of this 
crystallisation gave, on the addition of a quantity of the silver reagent, a 
precipitate which, after being kept in a porcelain crucible at 120° C. for five 
hours, was of the same weight as it gave when it was fused. This could only 
be a haloid salt of silver and, therefore, organic compounds of silver do not 
obtain in the precipitate. The filtrates from the first, third, and fifth 
precipitations of gelatin gave such silver haloid precipitates, but in quantities 
diminishing in the order named. 
Attempts were made to prepare nucleo-proteids in a pure form, but these 
were unsuccessful, simply because the one efficient precipitant of these 
compounds from their solutions is dilute hydrochloric acid and enough of this 
reagent always adhered to or was united with the precipitates to give a 
distinct silver chloride reaction. The same difficulty was experienced in the 
case of nucleic acid. 
It was not necessary, however, to prepare purified nucleo-proteids or nucleic 
acid, for when animal and vegetable tissues in fresh condition are treated with 
the silver reagent and then exposed to light, the nuclei, if normal, are never 
affected and, therefore, not only is haloid chlorine absent from nuclei, but also 
nucleo-proteids do not react with the silver salt. Further, as the head of the 
male element in the frog and Oniscus gives no reaction with the reagent, it 
may be inferred that the simpler compounds of nucleic acid are also unaffected 
by nitrate of silver. 
No attempt was made to isolate vegetable proteids in a form free from 
chlorides, but that they also do not give coloured products when treated with 
nitrate of silver and placed in the sunlight, seems to be clear from simple 
experiments which can be readily made on vegetable tissues. When thin 
sections of any succulent vegetable stem (e¢.g., of Zulipa) are treated with the 
reagent, sunlight brings out a deep reaction in every part of the preparation, 
not only in the protoplasm, but also very frequently in the cell walls, the 
nuclei alone, when normal, never exhibiting the slightest reaction, When, 
however, the sections were first placed for a couple of hours in 99 per cent. 
alcohol, no colour reaction whatever developed on treatment with the silver 
* The filtration had to be done very carefully, in order to remove organic compounds 
which unite with silver nitrate, and which are thus precipitated, but such silver 
compounds do not discolour in sunlight. 
