AND HOW TO USE IT. 31 



from the enemy, " air-bubbles " ; but whether or not there be air- 

 bubbles, it is of great value to boil the jelly and object upon the 

 slide, but care must be taken, or the mount may be ruined. If 

 boiling be chosen, a wood clip should be used, and the slide held 

 by it directly over, but not too close to the flame of a spirit-lamp. 

 It will at first begin to bubble from the centre outwards. If the 

 slide be now carefully watched, a very perceptible crack may be 

 seen and heard at this moment, when, without delay, the slide 

 must be withdrawn from the heat, and placed upon a cold surface 

 (a block of marble, or a brick previously soaked in cold water), 

 when the jelly will rapidly become cold and solid. 



Canada Balsam has largely given place to Balsam and Benzole, 

 Balsam and Chloroform, or Dammar, each of which medium has 

 advantages over the others for certain objects ; but our choice for 

 general work is Balsam and Benzole, which we have used for 

 years. For many descriptions of work, pure Canada Balsam, or 

 Balsam and Turpentine or Chloroform, or Dammar, are used for 

 less transparent and for stained tissues, rendering specimens which 

 are mounted in them very clear. The media required in mount- 

 ing from spirit are to be applied in the order given above, the 

 specimen being changed from watch-glasses containing them by a 

 section-lifter, after removing any excess of each fluid clinging to 

 the specimen by the back of the hand or a piece of blotting- 

 paper. The former is preferable, as less likely to cause any hairs 

 or pieces of cotton to touch the object. The specimen may 

 remain on the slide, and the medium applied by pipettes and 

 removed by the hand or blotting-paper after their action. Five to 

 ten minutes is usually sufficient time for a section to remain in 

 each fluid. 



To better explain the method of mounting, let us take some 

 objects from the animal kingdom — say parasites. It vvifl in most 

 cases be advisable to put them in liquor potassce for a short time. 

 When they have been softened and sufficiently reduced in colour 

 they must be well washed in water, and if they are brushed under 

 water with a stiff camel-hair pencil, the legs will frequently be 

 found right for mounting. The last washing- water having been 

 poured off, and methylated spirit added, let them remain in this 



