ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
129 
(2) Preparing- Objects. 
Investigating Histology of Vertebrate Liver.* — Dr. II. J. Berkley 
recommends the following as a method for showing the hepatic nerves. 
Liver tissue is cut into slices not more than 1 • 5 mm. thick, and while 
quite warm, is immersed in a saturated solution of picric acid, diluted 
with an equal volume of warm water. After remaining in this for from 
15 to 30 minutes, it is immersed for 48 hours in a hardening fluid com- 
posed of 100 parts of aqueous solution of bichromate of potash (saturated 
in sunlight) and 16 parts of 2 per cent, osmic acid ; this solution must 
be made several days before, and exposed to full sunlight. The 
specimens, however, must be hardened in absolute darkness at a tempe- 
rature not lower than 25° ; after hardening, the tissue is to be treated 
with 0*25 and 0*75 per cent, silver solutions in the usual manner, and 
allowed to remain in them for five or six days. After very rapid 
washing in running water they must be rapidly dehydrated, immersed 
for a few minutes in celloidin, placed on a cork, and the celloidin 
hardened in 75 per cent, alcohol in a closed jar ; this jar is to be cooled 
either by ice or under a current of cool water, so as to harden the cel- 
loidin as rapidly as possible. The sections are then to be cut under 
95° alcohol, rapidly dehydrated, cleared in oil of bergamot and mounted 
in xylol-balsam without cover-slip. The details obtained by this method 
are clearer than if the rapid silver process is used. 
Embryology of Chiton.^ — Mr. M. M. Metcalf found that of the 
agents used to fix embryos of Chiton the best results were, perhaps, got 
with an aqueous solution of picric acid to which sufficient sodium chlo- 
ride was added to bring the solution to the density of sea-water. In the 
early stages it was necessary to remove the chorion and the yolk with 
which all the cells were crowded ; for this purpose eau de Labarraquo 
(hypochlorite of soda) was used ; the embryos were passed from water 
into the ordinary eau de Labarraque, cold and of full strength ; after 
one-third to three-quarters of a minute they were removed to water, 
where the chorion soon swelled to more than twice its usual size, and 
could be removed by agitation of the water or by currents from a 
pipette. 
The sodium hypochlorite, if allowed to act for three minutes or more 
on the embryos, completely dissolves them. As it acts, however, much 
more rapidly on the yolk than on the protoplasm and nuclei, it is pos- 
sible, by regulating the time of immersion, to obtain embryos with the 
yolk almost wholly dissolved, and the protoplasm and nuclei almost un- 
injured. Though the method is crude it was the only way by which 
Mr. Metcalf was able to successfully get rid of the yolk. 
In staining early stages, after treatment with the eau the embryos 
were placed in weakly acidulated water, and passed thence into Dela- 
field’s hsematoxylin. As the acid washes out from the protoplasm 
before it leaves the yolk-granules, one may, by regulating the time of 
immersion, obtain preparations in which the nuclei and cell-boundaries 
are well stained, while the yolk-granules are unstained. 
* Anat. Anzeig., viii. (1893) pp. 772 and 3. 
t Stud. Biol. Lab. John Hopkins Univ., v. (1893) pp. 251-3. 
1894 
K 
