554 APPENDIX 



Marshall and Hurst's Practical Zoology. Borax carmine and hema- 

 toxylin are alcohol stains. Picrocarmine is a water stain containing 

 picric acid. After staining, the object must be washed with dilute 

 alcohol (for an alcohol stain) or water (for a water stain) to remove the 

 excess of stain. 



Small aquatic animals may be mounted alive in water ; parts of the 



tissues of larger animals which are to be examined in the 

 Mounting. living condition must be mounted in normal salt solution — ■ 



a 75 per cent, solution of common salt in distilled water. 

 This approximates more nearly to the natural fluids of the body, and 

 has not the injurious effect of pure water. Objects which are intended 

 for a prolonged examination should be mounted either in glycerin or in 

 some solid medium, such as glycerin jelly, which becomes solid when 

 cold, or Canada balsam, which becomes solid when dry. An object 

 may be placed direct from water into glycerin ; to be mounted in 

 Canada balsam it must first be dehydrated by soaking in absolute 

 alcohol, then steeped in oil of cloves or in xylol till the alcohol is 

 removed, and then placed in a drop of balsam upon the slide and 

 covered. The object should not be placed direct from water into 

 absolute alcohol, lest the diffusion currents set up by this strong de- 

 hydrant should injure it, but 30, 50, 70, and 90 per cent, solutions of 

 alcohol should be used successively for a period varying with the size 

 and density of the object. Thus the complete process for staining and 

 mounting in Canada balsam involves the successive use of : stain, 30 per 

 cent, or 50 per cent, alcohol to wash, 70 per cent., 90 per cent., and 

 absolute alcohol, xylol or oil of cloves, and Canada balsam. Very small 

 objects are best submitted to these processes on the slide, either under a 

 coverslip(p. 562) or not, but they are generally performed in ica/f/i-^/a««. 

 It is often important to study slices or sections of animals, organs, or 

 tissues. This may sometimes be done by placing the object (after 

 hardening in absolute alcohol, corrosive sublimate, or other hardening 

 agent) between two pieces of pith or carrot, and slicing off sections 

 freehand with a sharp razor. More often, however, it is necessary 



to use a section-cutting machine or microtome. The 

 Section- object is embedded before cutting in some fluid which 



cutting. solidifies, such as paraffin wax. The technique of this 



process should be learnt in the laboratory. It is 

 described in Marshall and Hurst's Practical Zoology and other books. 

 The following hints will be of service in using the microscope : — 



1 . Examine every object first with the low power, using 

 Hints on the t jj e high power afterwards if necessary. 



Microscope. 2> F°cus roughly with the coarse adjustment, and only 

 then use the fine. 



3. Use the utmost care to prevent the objective from getting dirty. 



It is damaged by cleaning. Never use the high power without 

 a cover glass. The eye-piece and objective may be cleaned if 

 necessary with chamois leather or silk. Canada balsam may 

 be removed by the very careful use of benzol or xylol, but in the 

 laboratory it is better to leave this to the demonstrator. 



4. The object may appear indistinct owing to the presence of dirt 



on the coverslip, the objective, or the ocular. If the dirt be 



