xvi INTRODUCTION 



III. ON THE METHODS OF KILLING ANIMALS. 



The method of killing is of considerable importance, and 

 careful attention should be paid to the directiong given at the 

 commencement of each chapter. 



It is important in most cases that the animal should die 

 in an expanded or relaxed condition. This is most readily 

 secured in the case of very minute animals, as Hydra and 

 the Protozoa, by suddenly deluging them with osmic acid, 

 which kills them instantaneously, before contraction can 

 occur. With animals of larger size, chloroform affords the 

 most convenient means for attaining the same end. 



Small animals, as the leech, earthworm, etc., may be 

 readily killed by dropping them into solutions of corrosive 

 sublimate, of chromic acid, or of picric acid, or into alcohol. 

 Crayfish may be killed by momentary immersion in boiling 

 water; and snails should be drowned, when they die fully 

 expanded. 



Many other methods are in everyday use, and the purpose 

 for which the animal is intended determines in many cases 

 the method of killing. 



IV. ON DISSECTION. 



The object of dissection is to separate the several organs 

 from one another, so far as is necessary to define their boun- 

 daries, and display their relations to one another. It consists 

 mainly in the removal of the connective tissue which binds 

 the parts together and obscures their outlines. 



The necessary instruments are the following : — 



1. Two or three scalpels, of different sizes. 



2. Two pairs of forceps ; one large and one small. Both 

 pairs should be straight, and should have roughened tips to 

 secure a firmer hold. 



3. Two pairs of scissors ; one pair large and strong for 

 general dissection, the other pair small for finer work. The 

 latter pair should have the blades either bent at an angle — 

 elbow scissors — or else curved. In selecting scissors, care 



