174 METHODS OP MICROSCOPICAL RESEARCH. 



enhances the effect and beauty of a representation, 

 if such details are carefully painted, and the rest of 

 the field delicately stippled up with indian ink, to 

 the edge of the circle. This applies to many sub- 

 jects threads of algse, or vegetable stems support- 

 ing such objects as fixed rotifera, polyzoa, &c., 

 introduced into a drawing, add greatly to the 

 interest and make most attractive pictures. Any 

 prepared mount or specimen should be as perfect as 

 possible, and considerable experience is necessary in 

 order to decide what is fairly good as a prepara- 

 tion and ivorth drawing. Common objects of 

 easy procurement from the woods, the garden, and 

 the stream, are exquisite models for the draughts- 

 man, their excellence, interest, and freshness are 

 necessarily superior to even the admirable results 

 now obtained by professional preparers, aided by 

 mechanical appliances, and rare skill in the use of 

 reagents and staining fluids. 



It is obvious that objects under polarised light, 

 are practically beyond the power of faithful delinea- 

 tion ; in all painting, whether in local tint or 

 shadow, purity of colour and the preservation of 

 brilliancy is of the first importance ; in order to 

 render, beyond a mere semblance, any subject under 

 the polariscope, it would be necessary, if such a 

 power were possible, to dip the pencil into light 

 itself, and an insuperable difficulty exists in the per- 

 manent preservation of the adjustments necessary 

 for future work, the slightest touch, or . alteration 

 of any part of the instruments, and even an obscure 

 change, beyond all control, in the quality of the 

 source of light alters the entire gamut and con- 

 sonance of colour, impossible to re-establish, yet, 



