INORGANIC SALTS. 31 



ETHEREAL OILS. 



Several volatile oils beside turpentine, which has 

 already been mentioned, find use in microscopy. 

 Oil of cloves and lemon oil are especially useful as 

 clearing fluids in the study of pollen. They are 

 also good preservative media for objects which can- 

 not be studied in water, but require a fluid of some 

 other refractive index. Since they decrease the re- 

 fraction they are very useful in the study of many 

 strongly refractive substances, by the aid of polar- 

 ized light. Preparations which have been in oil 

 must be washed with ether or chloroform and 

 afterward with alcohol before they can be placed 

 in water or glycerine. 



INORGANIC SALTS. 



CHLORIDE OF SODIUM (Table Salt). 

 A dilute aqueous solution 1 is used as a morpho- 

 logical reagent for the contraction of protoplasmic 

 bodies, a phenomenon which is to be attributed to 

 its avidity for water. Many other salt-solutions 

 have this property. A dilute solution of table salt 



1 Dippel : Das Mikroskop, L, p. 279. 



