xviii INTRODUCTION 



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 valuable 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, etc., 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 dissecting 

 it. In some cases the dissection may with advantage be per- 

 formed 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. 



9. If you get in a muddle, stop, and wash the dissection 

 thoroughly under the tap before proceeding further. 



Successive slices cut off an animal, or part of an animal, 

 with a razor are often exceedingly instructive ; this is especially 

 the case with the mussel and snail, and with the brains of 

 the rabbit and pigeon. The specimens must be previously 

 hardened with spirit or other reagent, and the slices should 

 be examined in water or spirit. 



V. ON INJECTION. 



The injection of coloured fluids into the blood-vessels or 

 ducts of an animal renders them much easier to see, an,d to 

 follow to their distribution. 



