138 AQUATIC MICROSCOPY FOR BEGINNERS. 



death. It is used by allowing a small drop to run 

 under the cover-glass and to mingle with the drop of 

 water containing the Infusoria. Any druggist can 

 make it, but caution him to use not more than half a 

 drachm (half a teaspoonful) of water, or you will be 

 terrified by his bill. If this small quantity is made it 

 is not expensive. 



To the half-drachm of water add as much iodide of 

 potassium as it can be made to dissolve, and to this 

 saturated solution add as much iodine as the solution 

 can be forced to dissolve. This ends the druggist's 

 part. It only remains for you to add enough of the 

 mixture to clean water to make the color a rather deep 

 amber.. The proper strength can be learned by experi- 

 ment. If it kills, and then destroys too quickly, add 

 more water; if it does not kill quickly enough, drop in 

 a little more of the iodine mixture. 



A weak solution in water of the/ifi^-chloride of iron 

 has been recommended for this purpose, but its action 

 is similar to that of the iodine solution, and no more 

 satisfactory. 



Although it is scarcely possible to preserve the ma- 

 jority of the Infusoria as permanently mounted ob- 

 jects, it is still possibly to preserve them alive pretty 

 successfully for some time, and to prepare an aqua- 

 rium in which they will thrive through the winter and 

 give the microscopist an ever changing supply. 



A specie-jar or a glass fruit-dish makes a good micro- 

 scopical aquarium, into which the gathering may be 

 poured and the contents left to themselves, a piece of 

 glass being placed over the mouth to prevent evapora- 

 tion, although this is not strictly necessary. Such an 

 aquarium presents a wider surface to the air, it is so 



