OF MICROSCOPIC OBJECTS. 



found to be as hard as resin, the softened and warm solution 

 may be now poured into a bottle, and when cool the benzole 

 added in sufficient quantity to make it of a desirable thick- 

 ness. Ten objects out of eleven contain air, or at least aie 

 full of minute holes which are necessarily filled with it ; so 

 that if they should be immersed in any liquid of thick 

 consistency, these cells of air would be imprisoned, and 

 become bubbles. The air, then, must be removed, and this 

 is usually accomplished by soaking for some time in turpen- 

 tine, the period required differing according to the nature of 

 the object. In some cases, the turpentine acts upon the 

 colour, or even removes it altogether, so that it must be 

 watched carefully. Often, however, this is an advantage, 

 as where the structure alone is wanted, the removal of the 

 colouring matter renders it more transparent. There are 

 objects, however, which retain the air with such tenacity 

 that soaking alone will not remove it. If these will bear 

 heat without being injured, they may be boiled in turpentine, 

 or even in balsam, when the air will be partly or totally 

 expelled. But where heat is objectionable, they must be 

 immersed in the turpentine, and so submitted to the action 

 of the air-pump. Even with this aid, sometimes days are 

 required to accomplish it perfectly, during which time the 

 air should be exhausted at intervals of five or six hours, if 

 convenient, and the objects turned over now and then. 



Many complaints are made concerning turpentine, both 

 as to its cleanliness and penetrating power. Most of these 

 spring from the fact that few substances in the market vary 

 so much as turpentine in purity ; all sorts of rubbish are 

 sold under this name, and now benzole is employed by many 

 in all cases where turpentine alone was once used. 



Sometimes the objects are so minute that it is impossible 

 to submit them to any soaking, and in this case they must 

 be laid upon the slide at once, and the turpentine applied 

 to them there. But it must not be forgotten that there are 

 some few which are much better mounted in such a way 

 that the balsam may thoroughly surround, and yet not 



