218 General Notes. [February, 
being taken that the shorter end of the arm, /, is uppermost. 
The string, g, should be tied to the stud upon which the arm, $, 
is supported, going thence round the groove, r, of the pulley, and 
back again to the hook at the longer and lower end of the arm, 
$, to which it should be tied. | 
Method of preparing the slide—Make by the aid of heat a vis- 
cid solution of white shellac in light colored creosote. Spreada 
smooth, thin and even layer of this solution on a clean dry slide 
with a camel hair brush or with the little finger. Arrange the | 
ribbon containing the sections on this slide while moist, and place 
it in the dry shelf of the water bath, which should be at a tem- 
perature slightly above the melting point of the imbedding ma- 
terial used. It should be left here until the creosote has evapo- 
rated and the imbedding material melted. Now allow the slide 
to cool, and then wash it with turpentine until all the imbedding 
material is dissolved. Canada balsam in chloroform or turpen- 
tine and the cover slip may now be applied in the usual manner. 
For convenience of mounting it is extremely important that the 
ribbon of sections should be quite straight, and in order to en- 
sure this it is necessary that the sides of the imbedding material 
from which the sections are cut should be quite parallel. The 
straight ribbon, when obtained, should be removed to some clean 
surface and there cut into lengths appropriate to the size of the 
cover slips used. It will be found convenient to use cover slips 
at least two inches long; indeed, a useful length for slides and 
oid slips is six inches for the former and four inches for the 
atter. 
~ 
A method of imbedding the specimen to be cit.—After the speci- 
men has been stained it should he left in ninety per cent alcohol 
for a few minutes, and thence transferred to absolute alcohol, 
there to remain until all the water is extracted. The length of 
time necessary for this varies greatly with the size of the speci- 
men. A three day chick, for instance, will require about an hour, 
larger specimens a day or more, in which case the absolute alco- 
hol should be changed occasionally. Some tissues may be trans- 
ferred directly from the absolute alcohol to turpentine, and thence 
in about two hours to the melted imbedding material. For deli- 
cate tissues, however, the following process, though longer and 
more troublesome, is greatly preferable. With a pipette intro- 
duce some chloroform to which two or three drops of ether have 
been added, under the alcohol in which the object is lying. The 
object will then float for some time at the junction of the alcohol 
and chloroform, and will finally sink into the chloroform when 
_ Saturated with it. If, as often happens in the case of embryonic 
: tissues, the object is lighter than the chloroform, it is not easy to 
x teli when the saturation is complete, but generally on shaking the 
bottle a saturated tissue can be temporarily covered by the chlo- 
