108 MICKOSCOPES FOK 



rays whicli are transmitted, I •\^'as unable to perceive it. Isthnia are 

 elightly iniluenced by polarised light. The larger Infusoria I have 

 not examined, nor am I aware that any infonnation is recorded on 

 this subject. 



Section VII. — On the Method of Feeding Infusoria with Coloured 

 Sulstances. — Select for this purpose such coloured substances as are 

 entu-ely fi'ee from metallic oxides, and not chemically soluble in 

 water. They must, however, be capable of a veiy minute mechanical 

 division. The substances generally used are cannine, indigo, and 

 sap-green, the &st being preferable. This material should be as 

 piu'e as possible. Take a piece or cake of it, and rub the corner 

 once or twice on the stage-glass, or what perhaps is better, the lower 

 plate of an aquatic live-box, having first moistened it -svith a drop of 

 water. The coloiu' requisite for the purpose is very small — only just 

 suiScient to render it ajjpreciable to the naked eye — for if there be 

 too much, the probability is, that the particles will be too large for 

 the creatures to imbibe. Having thus prepared the coloured food, 

 place a di'op of it beside a drop of the water containing the animal- 

 cules, but not so that they may come into contact ; then put on gently 

 the cover of the live-box, and lower it sufiiciently to flatten the two 

 drops of fluid, but not to force them to unite. Now place the live- 

 box under the microscope, and examine the animalcules as closely as 

 you can, and especially so as to ascertain that then- stomachs ai'e 

 coloui-less ; then press down the cover imtil the di-ops of fluid inter- 

 mix, which may be done under the microscope, and you wt.!! immedi- 

 ately perceive the creatiu'es ia great activity, and readilj- distinguish 

 the ciha and i)roboscides of those which possess them, while in a few 

 seconds their stomachs will be filled with the coloured substance. 

 Some animalcules, however, take a considerable time to efi^ect this, 

 but such is an exception to the general rule. 



Section VIII. — On the Mode of Drying and Preserving Infusoria. 

 — Although such exceedingly small creatures as animalcules, when 

 dead, lose many of their- characteristic leatiu'es, especially the soft- 

 bodied ones, yet, for the verification of some parts of their structure, 

 such as the mandicatory organs, muscular system, and visual points, 

 it is absolutely necessary to obsei-ve them in a quiescent state ; and 

 hence, a method of efi'cctuaUy di-ying and preserving them must be 



