12 VIEWS OP THE MICROSCOPIC WORLD. 



The best fluid for this purpose is, in most cases, Goadby's solution, which is 

 made by dissolving 4 ounces of coarse sea-salt, 2 ounces of alum, and 4 grains of 

 corrosive sublimate in 4 pints of boiling water. This mixture should be carefully 

 filtered before it is used, and, for all delicate preparations, it may be diluted with 

 an equal volume, or even with twice its volume of water. This solution must not 

 be used where any calcareous texture, as shell or bone, forms any part of the pre- 

 paration. It is very valuable for preserving anatomical specimens. 



A solution of chromic acid is well adapted for preserving many microscopical 

 objects. It is particularly useful for hardening portions of the nervous system 

 previous to cutting them into thin sections for examination. This solution is pre- 

 pared by dissolving a sufficient amount of the crystals of the acid in distilled water 

 to make the liquid of a pale straw-color. " It is often quite impossible," says Dr. 

 Carpenter, " to tell beforehand what preservative fluid will best answer for a par- 

 ticular kind of preparation, and it is always desirable, where there is no lack of 

 material, to mount the same object in two or three different ways, marking on 

 each slide the method employed, and comparing the specimens from time to time, 

 so as to judge how each is affected." 



Having alluded to the different ways of mounting objects, explained the mode of 

 preparing cells, and described the various cements and preservative fluids used for 

 microscopic purposes, we will now unfold more fully to what transparent objects 

 the different modes of mounting are adapted, and also the process of mounting. 



Mounting in the Dry Way. There are certain objects which, viewed by transmit- 

 ted light, are more advantageously seen when simply laid on glass than when im- 

 mersed in fluid and balsam. This is the case with sections of bones and teeth, 

 and with the scales of Lepidopterous and other insects whose surface-markings 

 are far more distinct than when mounted in any other way. These objects, how- 

 ever, must be protected by a glass cover, so attached to the glass slide as to keep 

 the object in its place, besides being itself secure. To effect the latter object, gold 

 size mixed with lamp-black can be employed. If the object has any tendency to 

 curl up, and to keep off the cover by so doing, it will be useful, while applying the 

 gold size, to press the two pieces of glass together by means of a spring clasp, 

 such as is used for fastening clothes to the line when drying. The slide should 

 be kept clamped until the gold size is sufficiently dry to hold down the cover by 

 itself. 



Another mode is to put a little dot of ink in the very centre of the slide, on the 

 side opposite to the object, and directly below the place it is intended to occupy, 

 so as to act as a guide during the process of mounting. Now place the object 

 carefully over the ink-dot, put the thin glass cover very lightly upon it, and fasten 

 it down with two or more strips of thin paper, which are to be pasted or gummed 

 round its edges. Two dry objects may be mounted upon the same slide. 



Mounting in Fluid. As a general rule, it is desirable that objects which are to be 

 mounted in fluid should be soaked in the particular fluid to be employed for some 

 little time before mounting; since, if this precaution be not taken, air-bubbles are 

 very apt to appear. 



The tissues of animals, parts of insects, and vessels of plants, and all such objects 

 as would lose their characteristics if prepared in any other way, are mounted in 

 fluids. The process is as follows : 



Clear the glass slide with a weak solution of ammonia or potash, and wipe it 

 dry with a piece of chamois leather or cotton velvet. Put a drop of the preserving 



