THE FROG 7 



to the tray; much is gained by leaving the object 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 in any case it is desirable to pin the animal to the tray, 

 see that the pins do not injure any important organs. Deli- 

 cate dissections should be made under water, which supports 

 the parts and gives better optical results. 



8. Dissection consists of separating and exposing the 

 parts with as little injury to them as possible. Only neces- 

 sary cutting should be done; the general rule is to cut noth- 

 ing unless you know what it is and why you cut it. In dis- 

 secting, 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 neces- 

 sary, make it as clean as possible avoid scrappy and hap- 

 hazard work. Do not peck the specimen. In cleaning blood- 

 vessels or nerves dissect along them and not across them, 

 and avoid laying hold of them with the forceps. 



9. 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. 



10. 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 towel or soft cloth and return them to 

 your locker. 



IV. USE OF THE DISSECTING LENS. 



The dissecting lens is designed to give a low magnifica- 

 tion with considerable working distance between the lens 



