INTRODUCTORY CHAPTER. 13 



fluid into the cell, then place the object in it with a small pair of forceps, and spread 

 it out very carefully with the point of a needle, taking care to remove any air-bub- 

 bles that may appear. 



The thin cover may now be placed upon the cell, one side being first brought 

 down upon its edge, and then the other, and if the cell has been previously run- 

 ning over with the fluid, it is not likely that any air-space will remain. All super- 

 fluous fluid is then to be taken up by blotting-paper, and the surface of the cell 

 and the edges of the cover made perfectly dry. When this is done, the cell may 

 be closed by cementing the edges of the cover and the sides of the cell by a thin 

 layer of size or asphaltum. 



Mounting in Canada Balsam. Among the various objects which are advanta- 

 geously mounted in this way are sections of shell, dry vegetable preparations, the 

 hard portions of the structure of insects, the horny tissues of the higher animals, 

 and also many organized substances, both recent and fossil. The great obstacle 

 encountered in mounting objects in Canada balsam is to keep them free from air- 

 bubbles, but by proceeding in the following manner this difficulty is usually over- 

 come : Take a curved glass tube, put some balsam into it. cork up the wide end, and 

 let it stand upon its end until wanted. Upon the metallic table place the glass slide, 

 light the spirit-lamp and put it under the table, so as to warm the slide throughout, 

 but not to overheat it. Then take the object, as a seed for instance, put it into some 

 spirits of turpentine, and let it wait there while the slide is becoming warm. The next 

 process is to remove the lamp and to hold the tube containing the balsam over the 

 flame, when the balsam will immediately run towards the orifice at the small end, 

 and a drop will ooze out. This drop should be placed on the centre of the slide, 

 and the seed taken out of the turpentine is then laid upon the warm balsam and 

 gently pressed into it with a needle. With the needle turn the seed about so as to 

 make sure that no air-bubbles are clinging to its surface. Now take a thin glass 

 cover, perfectly clean, warm it over the spirit-lamp, and lay it carefully and slowly 

 upon the balsam. Press it slightly down, and then, having placed on the cover a 

 small circle of pasteboard, put the slide within the clothes'-line clamp already men- 

 tioned, and then lay away the slide till the balsam has hardened. The superfluous 

 baJsam which will be found adhering to the edges of the glass cover may now be 

 removed by scraping it away with a knife, and then the slide more thoroughly 

 cleaned by wiping it with a rag moistened with spirits of turpentine or ether. 



Of Injections. The arrangement of the minute vessels or capillaries distributed 

 throughout various textures is not to be demonstrated, in all instances, by the usual 

 method of investigation, in consequence of the transparency of the walls of the 

 tube, and can only be well shown by means of injections of coloring matter. The 

 art of making these preparations is one in which success can only be attained by 

 long practice ; and better specimens can therefore be obtained from those who have 

 made it a business than are likely to be prepared by amateurs. Injections form 

 very interesting objects for microscopic examination. 



Any one who wishes to study more in detail and in all their minutiae the various 

 subjects which have just been discussed, can consult with great advantage such 

 works on microscopy as those of Quekett, Carpenter, Hogg, Beale, and others. 



