CH. X] MOUNTING MICROSCOPIC OBJECTS 321 



This is an excellent cleaning mixture and is practically odorless. 

 It is exceedingly corrosive and must be kept in glass vessels. It 

 may be used more than once, but when the color changes markedly 

 from that seen in the fresh mixture it should be thrown away. An 

 indefinite sojourn of the slides and covers in the cleaner does not seem 

 to injure them. 



MOUNTING, AND PERMANENT PREPARATION OF MICROSCOPIC 



OBJECTS 



498. Mounting a microscopic object is so arranging it upon 

 some suitable support (glass slide) and in some suitable mounting 

 medium that it may be satisfactorily studied with the microscope. 



The cover-glass on a permanent preparation should always be consid- 

 erably larger than the object; and where several objects are put under 

 one cover-glass, as with serial sections, it is false economy to crowd them 

 too closely together. 



499. Temporary mounting ; normal fluids. In a great many 

 cases objects do not need to be preserved; they are then mounted 

 in any way to enable one best to study them, and after the study the 

 cover-glass is removed, and the slide cleaned for future use. In the 

 study of living objects, of course only temporary preparations are 

 possible. With amoebae, white blood corpuscles, and many other 

 objects, both animal and vegetable, the living phenomena can best be 

 studied by mounting them in the natural medium. That is, for amce- 

 bse, in the water in which they are found; for the white blood cor- 

 puscles, a drop of blood is used and, as the blood soon coagulates, they 

 are in the serum. Sometimes it is not easy or convenient to get the 

 natural medium; then some liquid that has been found to serve in 

 place of the natural medium is used. For many things, water with 

 a little common salt (water 1000 cc., common salt 7.5 grams) is 

 employed. This is the so-called isotonic or normal salt or saline 

 solution. For the ciliated cells from frogs and other amphibia, 

 nothing has been found so good as human spittle. Whatever is used, 

 the object is put on the middle of the slide and a drop of the mounting 

 medium added, and then the cover-glass. The cover is best put on 

 with fine forceps, as shown in fig. 190. After the cover is in place, if 



