552 APPENDIX 



9. A miscroscope with the apparatus and reagents necessary for its 

 use (see p. 553). 

 In all cases in which it is possible, the animal should be examined 

 alive before dissecting, staining, etc. The shape and 

 Instructions • attitudes, movements, method of feeding, respiratory 

 Killing, ' movements, and so forth, should be carefully noted. It 

 must then be killed for detailed examination, which will 

 generally include both dissection and microscope work. Small animals 

 may be killed with a drop of some poisonous fluid, such as alcohol, 

 or solutions of corrosive sublimate or osmic acid (see below). Cray- 

 fishes are best killed by sudden immersion for a few seconds in boiling 

 water. For most other animals the best method is the use of chloro- 

 form either by placing them in a closed vessel with a bit of sponge 

 soaked in the liquid, or by holding a cloth similarly soaked over the 

 nostrils. Care should be taken that the exposure is long enough to kill. 

 Dissection is an art that must be acquired by practice. The fol- 

 Dissectlon lowing rules will be of use to the beginner : — 



I. Never start till you are sure what you are looking 

 for. 



2. Never cut anything till you know what it is. 



3. Fasten down the animal with pins to the bottom of the dis- 



secting dish or with nails to a dissecting board (according to 

 size) and keep the organs well stretched. 



4. Dissect along, not across, such structures as nerves and blood 



vessels. 



5. Keep your dissecting instruments sharp. They should be 



scrupulously cleaned and dried before being put away, and 

 fine instruments should never be used for coarse work. 



6. Small animals, including the frog, should be dissected under 



water, which should be changed as soon as it becomes cloudy 

 from the presence of blood, etc. The water supports and 

 keeps apart the organs, prevents their surfaces from glistening, 

 as they would do if they were merely damp with blood, etc., 

 and helps to keep them clean. You will find it of no advan- 

 tage to take the animal out of the water with the object of 

 seeing things in it more clearly. 

 Careful drawings should be made at all stages of the examination. 

 They should never be copied from books or lecture diagrams. The use 

 of coloured chalks in these drawings is not desirable, as it enables you 

 to represent an organ by a mass of colour without realising its outline. 

 The drawings should be of a good size in order to show detail clearly. 

 It is easier to draw a symmetrical object after making a faint line upon 

 the paper for the middle of the object. 

 The use of a compound microscope also requires practice. Such a 

 microscope consists of a stand bearing a horizontal stage 

 The Micro- for the object, a mirror to throw light through the object 

 soopa. from below by way of a hole in the stage, a diaphragm 



to vary the amount of light, a vertical tube through 

 which the object is viewed from above, and combinations of lenses 

 which are placed at the ends of the tube. Two such combinations must 

 be used — an objective or object glass which screws into the lower end of 



