THE MICROTOMIST'S VADE-MECUM

useful. He employs it as follows :'-Portions of muscle
(gastrocnemius of frog) having been very carefully teased out
in fresh serum are treated for ten to twenty seconds with
nitrate of silver solution of 2 to 3 per 1000, and exposed to
bright light (direct sunlight is best) in distilled water. As
soon as they have become black or brown they are brought
into 1 per cent. acetic acid, where they remain until they have
swelled up to their normal dimensions (the swelling induced
by the acid serving to make up for the shrinkage caused by
the nitrate of silver). They are then examined in a mixture
of equal parts of glycerin and water.
This process gives negative images, the muscular substance
is stained brown, except in the parts where it is protected by
the nervous arborescence, which itself remains unstained.
The gold-process gives positive images, the nervous structures
being stained dark violet.
543. Nerve-endings in Muscle (Wolff's method2).-The
pectoral muscle of a frog is excised and stretched over a cork
ring cemented to a slide; the cell is then filled with - per
cent. salt-solution; the preparation may then be studied even
with the highest powers.
It is sometimes advantageous to treat a stretched muscle
for twenty-four hours with 0-02 per cent. osmic acid; in this
case it must be stretched with hedgehog spines for pins. To
prevent the preparation from overstaining subsequently, it
may be placed for some time in Beale's carmine.
Chloride of gold and potassium were used of the strength
of 0-03 per cent. for twenty-four hours.
- Carl Sachs' method for demonstrating sensitive nerve-
endings was also employed. The living muscle is put for
twenty-four hours into 1 per cent. acetic acid, washed, put for
twenty-four hours into very dilute picric acid and studied in
dilute glycerin. The preparations so obtained are extremely
transparent.
I Ibid., p.. 810.   2 'Arch. Mik. Anat.,' xix (1881), p. 355.

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