XXIV INTRODUCTION 



Magenta is useful for staining fresh specimens, but the 

 stain is not permanent. 



Carmine is perhaps the most useful of all stains. It 

 affects different cells and parts of cells differently, and the 

 stain is [permanent. The most useful preparation of it is 

 Grenacher's borax-carmine : this should be used warm, and 

 the specimens after removal from it should be placed in acid- 

 alcohol for a few minutes or hours, according to their size. 



Picro-carmine has the advantage of being an aqueous 

 stain, and may therefore be used either for fresh or hardened 

 tissues. Immersion of the specimen in acid-alcohol for some 

 time after staining improves the effect. 



Hematoxylin (Kleinenberg's solution) gives excellent 

 results if used with due care, but a trace of chromic or other 

 acid may completely destroy the colour after the specimen is 

 mounted. 



Osmic acid, of which a 1 per cent, or ^ per cent, aqueous 

 solution is used, is both a hardening and a staining reagent. 

 It is only used with fresh tissues, and only with small speci- 

 mens. It kills Protozoa instantly, and after a time stains 

 their nuclei, though only faintly. Objects hardened with 

 osmic acid may be stained with picro-carmine. A mixture of 

 chromic and osmic acids forms a useful hardening reagent. 



Acetic acid, 1 per cent, solution, is useful for rendering 

 the nuclei of cells more distinct : it is used with fresh 

 specimens. 



VII. ON MICEOSCOPICAL EXAMINATION. 



The microscope affords the means of investigating the 

 structure of minute animals, and the finer details of those 

 of larger size. The microscopical examination of the special 

 organs of the larger animals is of great importance, and must 

 on no account be neglected. 



The microscope consists of a body and a stand. The body 

 is a tube of metal carrying the lenses, which are the essential 

 part of the instrument. 



The stand supports the body, in such a way that the 

 latter may be moved up and down without any lateral move- 



