KNIVES, ETC. TEST-BOX. xxiii 



selected, and may easily be removed with the mounted bristle (under the microscope) be- 

 yond the margin of the liquid. The remainder of the liquid is then wiped away with a 

 cloth, a little distilled water added to the small quantity of liquid left containing the object, 

 and the latter moved with the bristle into the middle of the slide. The liquid is then driven 

 off by heat, and the object is left on the slide ready for mounting. Or, when the matter is 

 dried upon the slide, any one of the minute objects being lightly touched with the bristle 

 will adhere to it, and by gently pressing or rotating the bristle upon the middle of a new 

 slide, the object will readily adhere to it. The Diatomacea3 may be easily isolated in this 

 way. 



Knives. Ordinary dissecting knives or scalpels. The handles should be sufficiently large 

 to allow of being firmly held. 



A particular and most useful kind of knife for producing thin sections of soft bodies is 

 that known as "Valentin's knife." It consists of two blades with their flat surfaces 

 parallel, set in a handle. The blades can be fixed at any distance apart, according to the 

 thickness of the section required. It is drawn across and through the substance, from heel 

 to point ; the section remains between the blades, and is then removed, either with forceps, 

 or the blades of the knife are opened under water, and the section floated upon a slide, also 

 immersed in the liquid. In the latter case, the action of the water upon the tissue must 

 not be overlooked. Valentin's knife is absolutely indispensable in the examination of 

 animal bodies. Some sections, especially of vegetables, are best made with a razor. 

 Black and white disk. A disk 3 or 4 inches in diameter, made of seasoned wood, and 

 upon one face of which a piece of white paper or card-board has been fastened by paste or 

 glue. One half of the paper or card-board is coloured black, the other is left white. This 

 is very useful in dissecting or separating minute portions of tissues ; if these are white, they 

 become much more easily distinguished than usual, when placed (on a slide) over the black 

 part of the disk ; if they are dark, over the white portion. 



Leaded cork. Some structures require to be dissected under water, as, e. g. those of in- 

 sects, &c. These should be fixed with pins upon a piece of cork, to which a plate of lead, 

 corresponding in size, has been fastened. In many cases it is advantageous to dissect these 

 tissues under the simple microscope. An aperture may then be made in the lead and cork, 

 and the tissue or structure stretched across the aperture, so that the light may pass through 

 it ; or it may be illuminated as an opake object by the aid of the bull's-eye. 



A trough, composed of five pieces of glass cemented together with marine glue, will 

 serve to hold the water and the loaded cork. 



Evaporating Dish or Saucer. It is advisable to keep one of these, with a flat bottom, 

 always at hand filled with distilled water, in which slides and covers that have been used 

 may be immersed. The remains of objects which have been examined are thus easily sepa- 

 rated from the glasses, and there is but little trouble in wiping the latter clean. If held 

 under a gentle current of water, all remains of tissues or test-liquids may be washed away ; 

 the glasses, from their gravity, remaining at the bottom. 



Test-box. A wooden box, holding from six to a dozen or more test-bottles, is indispen- 

 sably requisite. The box must be divided into partitions corresponding to the size of the 

 bottles, and the latter must be wedged between these partitions so that the stopper can 

 be removed without fear of disturbing the bottles. The box should be covered with a lid 

 furnished with hinges, so that no room may be required to place the lid when the box is 

 opened. The bottles will vary in size according to option, but they should be of at least 

 1 -ounce capacity. Each should have a stopper so prolonged as nearly to reach the bottom 

 of the bottle, its form being conical or rather fusiform. The advantages of this form of 

 stopper are, that a mere trace or several ordinary drops of the reagent may be applied to 



