II.] STRUCTURE OF BLOOD. 37 



e. The nucleus can seldom be made out, 

 except when the corpuscle is very extended. 

 Do not confound a heap of granules or a 

 protuberance with the nucleus. 



f. Choosing a corpuscle either elongated or 

 having several processes, watch carefully its 

 amoeboid movements ; make half a dozen 

 drawings of its outline at intervals of about 

 twenty seconds. 



g. When a drop of blood is first mounted the 

 colourless corpuscles are usually spherical, 

 they soon begin however to put out pro- 

 cesses; if it is desired to watch the move- 

 ments for any length of time a fresh drop 

 should be mounted and protected from eva- 

 poration in the following manner. With 

 a morsel of blotting-paper dry if necessary 

 the slide at the edges of the cover-slip. 

 Keep the cover-slip in place by gently 

 holding a needle against one edge, and, 

 with a small brush, brush carefully the 

 melted paraffin A. 1 (which melts at 39C.) 

 over the edges all round. The paraffin need 

 not extend more than \ or inch over the 

 cover-slip. 



3. a. With the aid of a camera lucida 1 make an 

 outline drawing of two or three red corpus- 

 cles; substitute for the specimen a stage 

 micrometer 1 , and being careful that the mi- 

 croscope and the drawing-pad are in the 



1 Cp. Appendix. 



