OF MICROSCOPIC OBJECTS. 167 
slide, and before it becomes dry pour over it two or three 
drops of pyroacetic acid for about half a minute. Tilt this 
off and replace by chloroform. Watch the effects, as before, 
under the microscope, and then cover with the Canada 
balsam solution and finish. These specimens, however, are 
not always permanent in their appearance, according to the 
results of some. 
Mr. Alfred Sanders gives his experience as differing some- 
what from this. He says—The brain, or other structure, 
being, as usual, hardened in chromic acid, the section is put 
for a short time in spirits of wine, and thence transferred to 
the creosote, which makes it transparent in a few minutes, 
when it is placed in Canada balsam. The balsam will mix 
easily with the creosote, or the solution in benzole may be 
employed. 
TRACHE® oF InsEcts, &c.—The nature of these was de- 
scribed in Chapter IV., but the method of procuring them 
was not explained, as this clearly belongs to dissection. 
The larger tubes are readily separated by placing the insect 
in water, and fixing as firmly as possible, when the body 
must be opened and the viscera removed. The tracheze may 
then be cleaned by the aid of a carmel-hair pencil, and 
floated upon a glass, where they must first be allowed to dry, 
and then be mounted in balsam. Mr. Quekett gives the 
following method of removing the trachez from the larva of 
an insect :—* Make a small opening in its body, and then 
place it in strong acetic acid. This will soften or decompose 
all the viscera, and the trachez may then be well washed 
with the syringe, and removed from the body with the 
greatest facility, by cutting away the connections of the 
main tubes with the spiracles by means of fine-pointed 
scissors. In order to get them upon the slide, it must be 
put into the fluid, and the trachez floated upon it; after 
which they may be laid out in their proper position, then 
dried and mounted in balsam.” If we wish them to bear 
their natural appearance, they must be mounted in a cell 
with Goadby’s fluid; but the structure is sometimes well 
