350 ACCESSORY APPARATUS 



moisture tli.-it surrounds their edges bo removed by blotting paper, 



llit-v will remain hi place when the microscope is inclined. An 

 wtmuLar <rll. lluii may In- used either :is ;\ 'live-box' or as a 'grow- 

 ing slide,' has lately been devised by Mr. Weber (U.S.A.). It is a 

 slip of plate-glass, of the usual size and ordinary thickness, out of 

 which a circular 'cell' of : j inch diameter is "-round, in such a 

 manner that its bottom is convex instead of concave, its shallowest 

 part being in the centre and the deepest round the margin. A 

 small drop of the fluid to be examined being placed upon the central 

 convexit v (the highest part of which should be almost flush with the 

 general surface of the plate), and the thin glass cover being placed 

 upon it. the drop spreads itself out in a thin film, without finding- 

 its way into the deep furrow around it ; and thus it holds-oil the 

 covering glass by capillary attraction, while the furrow serves as an 

 air-chamber. If the cover be cemented down by a ring of gold size 

 or dammar, so that the evaporation of the fluid is prevented, either 

 animal or vegetable life may thus lie maintained for some days. or. 

 if the two should be balanced (as in an aquarium), for some weeks. 

 Dipping Tubes. In every operation in which small quantities 

 of liquid, or small objects contained in liquid, have to be dealt with 

 by the microscopist, he will find it a very great convenience to be 

 provided with a set of tubes of the forms represented in fig. 304. 

 but of somewhat larger dimensions. These were formerly desig- 

 nated 'fishing tubes,' the purpose for which they were originally 

 devised having been the fishing out of water fleas, aquatic insed 

 larva-, the larger animalcules, or other living objects distinguishable 

 either by the unaided eye or by the assistance of a magnifying glass 

 from the vessels that may contain them. But they are equally 

 applicable, of course, to the selection of minute plants; and they 

 may be turned to many other no less useful purposes, some of which 

 will be specified hereafter. When it is desired to secure an object 

 which can be seen either with the eye alone or with a magnifying 

 glass, one of these tidies is passed down into the liquid, its upper 

 orifice having been previously closed by the forefinger, until its lower 

 orifice is immediately above the object; the finger being then re- 

 moved, the liquid suddenly rises into the tube, probably carrying 

 the object up with it ; and if this is seen to be the case, bv putting 

 t he linger again on the top of the tube, its contents remain in it 

 when the t ill ie is lifted out. and may lie deposited on a slip of glass, 

 or on the lower disc of the aquatic bo.\. or, if too copious for either 

 receptacle. inav lie discharged into a large glass cell. Ill thus 

 fishing in jars for any but minute objects, it will be generally found 

 convenieni to employ t he open -mouthed 1 11 bo (J ; those with smaller 

 orilices. A. 1>, being employed for ; fishing ' for animalcules, Arc., in 

 small bottles Or tubes, or for selecting minute objects from the cell 

 into which the \\ater taken up by the lube (' has been discharged. 

 It will be found \er\ convenient to have the tops of these last 

 blown into small tunnels, which shall be covered with thin sheet 

 indiarubber, or 1op|ed with indiarubber nipples, which bv com- 

 pression and expansion can then lie regulated witli the greatest 

 nicet v. 



