230 MOUNTING OF OBJECTS. 



pressing this down wherever the balsam happens to he thickest, 

 and endeavoring to drive all air-buhhles before a wave of liquid, 

 until they are entirely expelled, or at any rate are driven beyond 

 the margin of the section. If this operation be not at once suc- 

 cessful, either a few large air-bubbles, or a great number of 

 smaller ones, which cannot be got rid of by gentle pressure, 

 being visible between the surface of the section and the cover- 

 ing-glass, it is better at once to remove the cover by gentle 

 warmth, and to repeat the operation with an additional supply of 

 balsam, rather than to attempt to drive out the bubbles by any 

 manipulation. Whatever treatment be adopted, special care 

 should always be taken not to apply so much heat as to melt the 

 hard balsam beneath the section, 1 or to boil the thin balsam above ; 

 in the former case, the loosening of the section from the glass is 

 very apt to be followed by the detachment of some portions of it 

 from the rest, whilst the glass cover is being pressed down ; and 

 in the latter, the production of bubbles very seriously embar- 

 rasses the operation. If the heat should unfortunately be carried 

 so far as to boil the cement beneath the section, there will be little 

 chance, if its area be large, of getting rid of the bubbles thus 

 produced, without removing it altogether from the glass to which 

 it was attached, or, at any rate, without pushing it along the 

 glass, in such a way as to slide it away from the bubbles ; in that 

 case, the part towards which it is moved should always be well 

 supplied with balsam, and the bubbles that remain should be 

 drawn away or broken with the needle-point ; after which, the 

 section being slid back to its original position, it is probable that 

 no bubbles may be found beneath it. In cases, however, in 

 which the appearance of the preparations is an object of much 

 consideration, and in which the tenacity of the substance and 

 the small size of the section prevent much risk of its breaking 

 in the transfer, it may be loosened from the glass to which it 

 was first attached, either by heat, or by soaking in ether. The 

 former being the simplest and readiest method, is the one most 

 commonly practised ; the only difficulty lies in lifting oif the 

 specimen without breaking it ; and this may best be done, by 

 means of a camel-hair brush dipped in oil of turpentine. The 

 glass to which the section is to be transferred, should have a 

 large spot of liquid balsam laid in the proper place ; the object 

 is to be laid on this, and its upper surface covered with the like 

 balsam ; and then, the thin glass cover being placed upon it, this 

 is to be gently pressed down in the manner already described. 

 If ether be had recourse to, the slide should be placed in a wide- 

 mouthed bottle of that liquid, which should then be corked or 

 stopped ; and after a time, the section will be found to be lying 

 detached in it, whence it may be taken up either by the forceps 



1 It will often be found convenient to turn the slide with the face downwards, and 

 to apply a gentle heat directly to the thin glass cover, and to the balsam above the object, 

 instead of heating this through the glass slide and the balsam beneath it. 



