INFUSORIAL ANIMAT.CITLES. Ill 



niinutes the earth and sand will sink to the bottom of the glass, and 

 the shells being filled with uir, will float upon the surlace, and may 

 be removed b)^ gently introducing a slip of glass under them. 



Section XI. — On moimtiuci Infmoria permanently in fluids. — By far 

 the greater number of Infusoria are entii'cly destroyed when dried, 

 some, however, of the larger kinds, may be preserved in gum water, 

 which, when diy and indm^ated, wiU last a long time, if kept from 

 mildew. Canada balsam will preserve some few, but tliis latter plan 

 is specially applicable to the loricated class. 



In moimting objects in Canada balsam, it is requisite to have it, 

 as also yoiu' glass slides, kept warm. The slide, vnih. objects on it, 

 shoidd be held over a small flame, and a di'op of the balsam allowed 

 to fall upon it. Wlien this is sufficiently heated, the whole should 

 be covered with a thin plate of glass, and placed in a warm situation 

 until it becomes hard. 



As many organisms cannot be preserved in gum or balsam, and 

 alter and change theii- forms when diy, it becomes essential to theii- 

 due preservation to mount them (as it is technically termed,) in a 

 fluid. To effect this piu-pose effectively, two particulars are ne- 

 cessary to be observed — fu'st, the selection of the fluid ; and second, 

 the mechanical contrivance for permanently enclosing it with the 

 specimen. 



The requisite qualities in a preser\'ing fluid are — fb'st, that its 

 refractive power shall be such that it wiU permit the outline or 

 boundary of the specimen to be distinctly seen. This cannot be, if 

 its refractive index is the same as the object enclosed. When the 

 object is surrounded by a mucus-like envelope, this consideration is 

 important. Second, that it wiU not change the colour of the speci- 

 men, or decompose any of its delicate parts. In the Bacillaria, the 

 green matter, called by botanists endochrome, and which is so beau- 

 tiful a character in the Besmidiem, is soon injured by corrosive fluids. 

 Third, the fluid must not facilitate or permit the growth of minute 

 fungi, or the development of any organic filaments, as the germs or 

 spores of these minute beings are almost eveiywhere present, and, 

 indeed, it is hopeless to procure specimens free from them. 



The iii'st two conditions are best complied with by the use of dis- 



