292 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ear adhering to it by the eighth nerve, was removed. By careful 
dissection it is possible, when desired, to remove the entire ear intact. 
The material was then transferred to 12 % formalin containing 1% 
nitric acid, for the decalcification of the otoliths, which cannot readily 
be removed by dissection without injury to the sensory areas. It has 
been found that 24 hours is an adequate time for decalcification. ‘The 
carbon dioxide evolved acts as a float for the ear sac and causes it to 
rise to the surface of the fluid. ‘The gas must therefore be removed, 
by gentle pressure, through a suitable opening made at some non- 
sensory portion in the wall of the ear sac. ‘This opening also serves to 
admit to the interior of the ear the impregnating and reducing fluids 
used later, thus insuring the contact of the inner ends of the sense cells 
with these fluids. After decalcification it is necessary to rinse the 
material in flowing water for several hours, to remove all traces of 
nitric acid. 
The material is now transferred to a 2 % solution of silver nitrate, 
in which it is allowed to remain for about 24 hours, after which it is 
removed and immersed in an ammoniacal solution of silver oxide, 
commonly known as Bielschowsky’s fluid, for a period varying with the 
kind of material that is being used. ‘This is followed by a rapid rins- 
ing, to remove the excess of the fluid from the surface, after which the 
material is transferred to a 20% solution of formalin. After 12 hours 
or more in this fluid the material is rapidly dehydrated, cleared, im- 
bedded in paraffin, sectioned, and mounted in balsam, in the usual way. 
An essential feature of this method of silver impregnation is that 
the nerve paths become occupied by a finely divided precipitate of 
metallic silver, set free from the silver compound by the reducing 
action of the aldehyde. In this it differs from the Golgi method, in 
which there is present more or less of silver chromate, a crystalline 
product which is probably responsible to a large degree for the notori- 
ously capricious results obtained by that method. It differs from the 
somewhat analogous reduction method devised by Ramén y Cajal 
(:04*) in three rather important particulars: (1) ammoniacal solution 
of silver oxide is used for impregnation, in addition to the silver nitrate 
solution common to both methods; (2) the reducing agent employed 
is formaldehyde, instead of the reagents commonly used in developing 
photographic plates; and (3) all the processes are carried on at room 
temperature, rather than at the higher temperatures required by Ramén 
y Cajal’s method. 
Bielschowsky’s fluid is prepared as follows: ‘To a suitable quantity 
of a 2% solution of silver nitrate a few drops of a 40% solution of 
