62 THE AMERICAN MONTHLY [March, 



the structure is rendered still more distinct, and if the specimen be only 

 thin enough the minutest detail is thus finally brought into view. 



Let us suppose, further, that this bit of paper consists of two or 

 three, or more kinds of fibres — say silk, cotton, and linen — all of the 

 same color and so interwoven with each other that it is impossible for the 

 eye to follow the ramifications of either material. It is plain that if we 

 can find a dye or stain which will attack the cotton and not the silk oi- 

 lmen, or vice versa, or that stains cotton one shade or hue, silk an- 

 other, and linen another, the problem of differentiating the elements 

 which enter into the structure is a very simple one. 



With these two hints as to the reason why the sections are put 

 through the next two processes, and leaving the philosophy of the same, 

 we will resume the progress of our slide toward completion. 



The sections as they fall from the knife are received in a vessel filled 

 with fluid — water, glycerine, or alcohol, according' to circumstances, 

 and when a sufficient number has been cut we pick out one of the 

 thinnest and best and place it in the staining fluid, where we will leave 

 it while we prepare the glass slip upon which it is to be mounted. 



We take for this purpose a piece of clear glass 3 inches long and 1 

 inch wide, the edges of which have been ground and polished, and 

 placing it on an instrument called a turn-table with a pencil dipped in 

 cement (the nature of which depends upon the fluid which we shall use 

 as a mounting medium), we spin a ring in the centre of it. This ring 

 is large enough and deep enough to receive the object to be mounted, 

 and should be allowed to get quite dry before the slip is used. The 

 object, in the meantime, has been removed from the staining fluid and 

 put through a number of little details to fix the stain, clear away the 

 embedding material, etc., and is now soaking in the fluid which is to 

 serve as a mounting medium, the functions of which are to render the 

 object transparent and preserve it against decay. In this instance we 

 will suppose that glycerine has been chosen as a medium. The ringed 

 slip, thoi'oughly cleaned, is now placed on the mounting box (a frame 

 with a glass top and provided with a mirror so arranged as to throw 

 light upwards through the top and object laid on it) and a drop of pure 

 glycerine is allowed to fall in the centre of the ring ; the object is quickly 

 transferred from the glycerine bath in which it has been laying, placed 

 on the drop of glycerine already on the slip, and arranged in the posi- 

 tion it is henceforth to occupy. Air bubbles are gotten rid of, the cover 

 glass is applied and clamped in position ; surplus glycerine is washed 

 away and the slip and cover glass carefully and thoroughly dried with 

 prepared blotting-paper. The clamp holding the cover glass in place 

 is now removed and the slip transferred back to the turn-table, where a 

 ring of cement is spun around the edges of the cover glass. This ring 

 is allowed to dry, and the slip is again washed and carefully dried be- 

 fore a second layer of cement is applied. The final touches, which 

 vary according to the taste, skill, etc., of operator, are then given to the 

 slide ; it is labelled, and, if the job is properly done, is good for an in- 

 definite number of years. 



Such, in brief, is the ordinary routine of processes usually employed 

 in making a mount of a pathological or histological specimen of the 

 soft tissues. There are many minor operations, matters of detail, en- 

 tirely omitted or barely alluded to in the foregoing sketch, while many 



