180 



The Microscope. 



under so gradually that the object, even a minute Infusorian, will 

 not be moved from the field, the inward rush of the current being 

 tempered by the cement ring. This supply can be easily added by 

 one hand holding the wet brush while the eye is intent at the ocular, 

 the secret of success here being in not having too large a brush and 

 in not filling it too full of water. At the beginning of daily evening 

 work the brush is wetted and thrown on the table to become 

 thoroughly moistened, when a single dip into the tumbler, with a 

 slight shake to prevent dripping, takes up enough, although some 

 pressure of the brush against the slide may be needed to squeeze 

 out a small drop. It is better to make several journeys to the 

 tumbler than to lose the object. A dipping- tube adds too much at 

 once, and cannot be so readily controlled as a brush. 



— In studying the moiphology of minute 



animal organisms, I use only a shallow, shellac 

 cell with about one-foui'th of the ring scraped 

 from both the upper and the lower margins, 

 thus leaving two curved supports for the 

 square cover, one on each side. (The dia- 

 gram. Fig. 1, shows the arrangement, the 

 shaded parts representing the remnants of the 

 cell.) This gives the enclosed drop with its 

 animal life plenty of air, and facilitates the 

 application of the wet brush at the point 

 where the square cover projects beyond the 

 lateral cell wall. In this simple aflFaii* I have 

 frequently kept Infusoria and other small 

 creatures alive and well from early in the 

 evening until after midnight, and when com- 

 pelled to leave them have washed them into 

 the aquarium in as good condition and as lively as when fii'st im- 

 prisoned. Here the secret of success consists, I think, in leaving 

 enough of the cement ring to properly support the cover, and to 

 lessen the force of the inflowing water supply, and also in having 

 the cell shallow or deep according as the animals are microscopically 

 small or large. Much depends on the depth of the cell in all cases. 

 A comparatively large Infusoi'ian, a Rotifer or a Ch?etonotus can be 

 injuriously hampered in its movements and in the proper perform- 

 ance of its functions by a cell of insufficient depth, and a good 

 objective can, as the reader knows, be greatly hampered in its func- 

 tions by a cell of too great depth. 



