THE FROG 5 
while being dissected, but in the case of an animal as large as a 
frog it is seldom advisable to pin the specimen to the tray; much 
is gained by leaving the specimen free so that it can be turned 
over as occasion demands, or held in the hand in such a way as to 
expose the parts being studied. If it is found desirable to pin the 
specimen to the tray, see that the pins do not injure any important 
organs. Delicate dissections should be made under water, which 
supports the parts and gives better optical results. 
4. Dissection consists of separating and exposing the parts with 
as little injury to them as possible. Only necessary cutting 
should be done; the general rule for dissecting is to cut nothing 
unless you know what it is and why you cut it. In dissecting it 
is often necessary to remove the connective tissue which binds the 
other parts together. The instruments in most constant use 
should be forceps, needles and seeker, rather than scalpel and 
scissors. When an incision is necessary, make it as clean as 
possible—avoid scrappy or haphazard work. Do not peck the 
specimen. 
In cleaning blood-vessels or nerves always dissect along them 
and not across them, and avoid laying hold of them with the 
forceps. When separating muscles dissect along their fibers and 
not across them. 
5. Keep the parts being dissected clean: free from debris, 
mucus, etc. Delicate dissections may be washed with a gentle 
stream of water from a pipette. 
6. Scalpels should be kept sharp. A whetstone is provided 
and students will be instructed how to use it. 
7. Instruments should be used only for the purposes intended. 
8. The student should provide a towel for individual use. 
9. At the close of the laboratory period return your specimen 
to the preserving fluid; rinse out your tray and place it on edge in 
the rack to dry; clean your instruments, wipe them dry with a 
soft cloth or towel and return them to your locker. 
IV. PRELIMINARY EXERCISE ON THE USE OF THE COMPOUND 
MICROSCOPE. 
A. With the aid of an instructor identify the following parts 
of the microscope: Stage, diaphragm, mirror, tube, ocular or eye- 
piece, objective, coarse adjustment, fine adjustment. 
