XX INTRODUCTION. 



one position, otherwise the image of the object will move. Also the field and the paper 

 must be illuminated to nearly the same extent. One of the screens mentioned at page xxv 

 is very useful for excluding extraneous light. 



Live-Box and Growing -Slide. — The live-box is an apparatus in which portions of liquid 

 containing infusoria and other small animals or plants, can be confined so as to prevent eva- 

 poration and allow of their being watched in a living state. 



A better apparatus however for this purpose is the growing-slide. This consists of a 

 piece of stout plate-glass, 5 inches long and about 2 wide. A circular aperture, of about the 

 diameter of a test-tube, is made near one end of it. A little glass cup, formed of a portion 

 of a test-tube cut ofi' three-fourths of an inch from the closed end, and slightly less in 

 diameter than the aperture, is then fitted into the latter, either by pieces of cork, or 

 by a rim consisting of a glass ring forming a neck to the cup, or in any other w ay. The cup 

 should project about one-fourth above the surface of the slide ; and at one portion of its 

 margin a little groove should be ground, in which two or three threads of a lamp-wick can 

 be placed. The cup should be covered with a circular plate of thin glass, larger than its 

 mouth, and prevented from falling oif by a disk of cork fitting the mouth, and fastened to the 

 plate by marine glue ; or the cup may be closed wdth a common cork, the only objection 

 to this being that the mouth of th# cup is apt to be split. The manner in which the slide 

 is used is this ; supposing we wish to follow the changes undergone by some minute alga 

 or infusorium which we have just detected in a drop of liquid. It is placed upon a slide 

 and covered with thin glass ; the slide is then laid upon the growing slide in such manner 

 that the longer dimensions of the two are in the same direction ; a little ledge consisting 

 of a strip of glass fastened by marine glue to the growing slide will serve to rest the shde 

 against and prevent its becoming displaced. Distilled water, mixed with a small proportion 

 of the water in which the organism was living before being transferred to the slide, is next 

 put into the cup, and a few threads of lamp-wick cotton, thoroughly moistened with 

 distilled water, are then so placed that one end is immersed in the cup whilst the other is 

 brought into contact with the edge of the liquid in which the object is immersed. Thus, as 

 the water evaporates from beneath the thin glass, the threads will aff"ord a continuous supply, 

 and the threads will not become dry until the whole of the liquid in the cup has become 

 absorbed by them and evaporated. In this way we obtain the requisite conditions for the 

 continued growth of aquatic organisms. Care must be taken however that the thin glass 

 presses but slightly upon the object, and that the threads come as little as possible into con- 

 tact with the portions of the slide lying betw een the cup and the thin glass. If the thin 

 glass cover to the cup fit tightly, and the thread be passed through the notch in the cup, no 

 loss will take place by the direct evaporation of the liquid in the cup. If living organisms 

 are kept in this apparatus, they must have the influence of light. 



Compressor, an instrument for the regulated compression of a minute object. The same 

 effect can be produced by a well-made live box ; or by pressure directly applied to the thin 

 glass covering an object by the handle of a mounted needle. 



Cabinet. — A box or cabinet, containing a number of drawers, will be requisite for holding 

 the objects. Each di'awer should be numbered or labelled to facilitate reference. The ob- 

 jects should lie flat in the drawers, so that each may be found when required without loss of 

 time. The cabinet should be furnished with two folding doors, so as to exclude dust as 

 much as possible. It should also be made of thoroughly seasoned wood, oak or mahogany 

 being the best ; if made of deal or cedar, the vapom* of the volatile oil of the wood will in- 

 sinuate itself beneath the thin glass cover and the slide in those objects which are mounted 

 in the (h-y state, and condensing upon them and the objects, will obscure and spoil them. 



It may be remarked here, that the names of objects shoidd always be written upon labels 



