xxii INTRODUCTION. 



Animals, such as the cockroach, which are difficult to fix 

 with pins, may be cemented down with melted wax, or they 

 may be half imbedded in a plate of paraffin, and the plate 

 then fixed down with pins in the dissecting-dish. 



For fine work a dissecting microscope affords great 

 assistance. The pocket-lens may be turned into one by 

 fitting one end of a wine-cork into the handle or case of the 

 lens, and passing a stout pin transversely through the other 

 end. The pin should be stuck upright into the dissecting- 

 board, with the lens over the part to be dissected : focussing 

 is effected by sliding the cork up and down the pin. A lens- 

 holder is, however, more convenient. 



The following rules for dissection should be carefully 

 observed : 



1. Before commencing a dissection, fix the animal down 

 firmly to the dissecting-board or dish. 



2. In fixing an animal with pins, stick them in obliquely, 

 so that their heads do not get in the way or obscure the 

 dissection. 



3. Dissect under water, unless the animal is too large. 

 Change the water as soon as it gets dirty. A gentle stream 

 of water allowed to play upon the dissection is often a valu- 

 able aid. 



4. Never cut away anything until you are quite certain 

 what it is you are removing. 



5. Put the part you are dissecting slightly on the stretch. 

 This applies more particularly to blood-vessels, nerves, ducts, 

 and muscles. 



6. In cleaning blood-vessels, nerves, &c, dissect along 

 them, and not across them ; and avoid laying hold of them 

 with the forceps. 



7 The dissection is in many cases greatly facilitated by 

 placing the specimen in spirit for a day or so before dis- 

 secting it. In some cases the dissection may with advantage 

 be performed under spirit. 



8. Always keep your instruments clean and sharp. Be 

 careful not to blunt your fine scissors or scalpels by using 

 them for cutting hard parts. 



