350 ACCESSOKY APPARATUS 



moisture that surrounds their edges be removed by blotting paper, 

 they will remain in place when the microscope is inclined. An 

 annular cell, that may be used either as a ' 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 ground, 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 

 convexity (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-on 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 be 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 1 

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

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

 larvae, the larger animalcules, of 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 tubes 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, by putting 

 the finger again on the top of the tube, its contents remain in it 

 when the tube is lifted out, and may be deposited on a slip of glass, 

 or on the lower disc of the aquatic box, or, if too copious for either 

 receptacle, may be discharged into a large glass cell. In thus 

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

 convenient to employ the open-mouthed tube ; those with smaller 

 orifices, A, B, being employed for 'fishing' for animalcules, ifec., in 

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

 into which the water taken up by the tube C has been discharged. 

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

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

 indiarubber, or topped with indiarubber nipples, which by com- 

 pression and expansion can then be regulated with the greatest 

 nicety. 



