ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
239 
the outside. The capsule proper has a double rim, the intervening 
furrow or channel being intended for the closing material. The cover, 
which dips into the channel, has the edge bent down so as to more effec- 
tually prevent entrance of germs. Very much the same result would be 
attained by using three capsules of different diameters, the one of middle 
size being used as the cover. 
Sensitive Litmus-Paper.* — According to Herr Sachs, in order to 
obtain a sensitive litmus-paper, it is necessary to remove the brown- 
violet pigment from the litmus ; and he recommends that, after the litmus 
has been macerated for 12 hours in water, the strained fluid should be 
evaporated down in a water-bath to the weight of the litmus used. It 
is then to he diluted with three parts of 90 per cent, alcohol, and after 
having been acidulated with hydrochloric acid, to be allowed to stand for 
48 hours. The azolitmin is then found as a brown sediment deposited 
on the bottom of the vessel, while the violet pigment remains dissolved 
in the alcoholic fluid. The precipitate is washed with acidulated water 
until the filtrate, tested with ammonia, gives a blue colour without a trace 
of violet. It is then dissolved in ammonia in the proportion of 1 to 3 * 5, 
neutralised, and used for saturating bibulous paper. To render this 
solution durable, 10 per cent, alcohol should be added. 
Delicacy of the Biological Test for Arsenic.f — Dr. F. Abba highly 
recommends Gosio’s test for arsenic. This test consists in growing 
Penicillium brevicaule in contiguity with a piece of the suspected sub- 
stance. If arsenic be present, the odour of garlic soon becomes apparent. 
The test is not only delicate, but rapid, and has been used by the author 
for detecting the presence of arsenic in urine, paper, gas, and hides. 
The procedure is simple. Two or three pieces of potato with a hole 
in the middle are placed in a Petri’s capsule. Into each hole is inserted 
a small piece of the suspected material (say a piece of hide or skin 
1 cm. long by 0*5 cm. broad), and the whole sterilised for 20 minutes at 
115° C. When cool, about 0*5 ccm. of water in which are suspended 
spores of Penicillium brevicaule is poured over the potato. The culture 
is kept at room temperature, and when opened in 24 hours, the charac- 
teristic smell of garlic is perceptible. 
The result may be hastened by incubating at 37° ; hut in this case, 
and more especially if several examples are being tested at the same 
time, the atmosphere of the laboratory becomes so impregnated with 
the garlicky odour as to render it difficult to say from which capsule 
the smell proceeds. As an example of the delicacy of the test, the 
author states that he cut from the same skin two pieces, one 5 sq. cm. 
and the other 1 sq. mm. in area, and examined the former by Marsh’s 
test and the latter by Gosio’s. The chemical test failed, while the bio- 
logical succeeded. 
* Wiadom. Farmac. ; Pharm. Zeitsclir. Russl., 619. See Zeitschr. f. ang. Mikr,, 
iv. (1898) p. 215. t Centralbl. Bakt. u. Par., 2 te Abt., iv. (1898) pp. 806-8. 
