METHODS OF INVESTIGATION. 



115 



for the year 1693, embodies the following highly interesting data. Having 

 recorded the results of the application to Infusoria, with a needle's point, of 

 various substances producing no very important effects, he says—" Tincture 

 of salt of tartar {tartaric acid?) put with them in the same manner kills 

 them more immediately, but yet they will be first so sick or so affected, 

 call it what you please, as you may see by a surprising convulsive motion, 

 they will grow faint and languid apace, and you may see them fall to the 

 bottom of the drop upon your object plate, dead but in their own shape 

 that they were in before you applied your needle, and will neither be flat 

 as with spirit of vitrol, nor cylindrical as with common salt liquor ; but lie 

 dead in the same shape as before you put in your needle with the salt of 

 tartar. — Sack will kill them, but not so speedily as the other liquors." 



Methods of Investigation. 



To the working microscopist a hint or two will probably prove accept- 

 able with reference to the mechanical means that may be most advan- 

 tageously resorted to in the investigation of the structure and life-histories 

 of the more minute, and comparatively unfamiliar, representatives of the 

 Infusorial series. These, as typified by the several orders of the class 

 Flagellata, necessarily demand in conjunction with the high-power object- 

 glasses that are indispensable for their correct appreciation, more delicate 

 methods of manipulation. 



A chief obstacle encountered in the employment of these short-focussed 

 lenses presents itself at the outset in the matter of penetration. However 

 thin may be the covering glass employed, it rarely fulfils the needs of the 

 investigator, and mostly causes both inconvenience and loss of time on 

 account of its extreme brittleness. Where the objects under examination 

 are attached to more solid substances, such as the stems of water plants, 

 this rigidity and brittleness of the covering glass hampers progress in a most 

 provoking manner, and materially restricts the limits of clear vision. The 

 unsuitability of ordinary covering glasses for the special investigations here 

 alluded to, was long since recognized by the present author, and a substitute 

 provided that has been productive of the most satisfactory results. The 

 material utilized for this purpose was no other than the one extensively 

 employed, previous to the introduction of specially prepared glass, for the 

 permanent mounting of microscopic objects. This substance, represented 

 by ordinary talc as extensively used for gaselier shades, may with a little 

 practice be split into lamina; of such extreme tenuity that they may be 

 blown away with the lightest breath, while for perfect evenness and trans- 

 parency they will compare favourably with the finest manufactured glass. 

 With the employment of these talc-films the investigation of Infusoria with 

 the tV, ^V, or even the sV-inch objectives becomes a comparatively easy task. 

 The material in question possesses the further considerable advantages of 

 bending readily and permitting the object-glass to be brought close down 



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