100 THE AMERICAN MONTHLY [Mar 



part of g-lacial acetic acid. Pour it upon the org-anism 

 while its org-ans are extended and, before it has had time 

 to retract them, death will ensue. Then take up as much 

 as possible of the killing- fluid and replace it with thirty 

 per cent alcohol. Repeat and add alcohol till sure the sub- 

 limate and acetic acid are gone. This will be accomplished 

 in half an hour. Objects too minute to be seen readily or 

 found easily may require some other reagent. 



To Mount Ameba. — Dr. Overton of Zurich University 

 gives the following- : Having killed by usual methods bear 

 in mind the brittleness of such objects. Transfer the ob- 

 ject with a particle of alcohol upon a clean cover glass. 

 Upon a thin piece of cork place the cover g-lass containing 

 the ameba having- the cork smaller than the glass so that 

 the latter may project over on all sides and prevent the 

 alcohol from running- off from the slip. The cork is placed 

 on a little bridge of lead and the latter in a small dish. 

 Pour into the dish enoug-h absolute alcohol to reach half 

 way up to the slip. Cover and set away over night. The 

 next day, it will be discovered that absolute alcohol has re- 

 placed the thirty per cent alcohol and the ameba has been 

 dehydrated^ — ^freed from all trace of water. This is neces- 

 sary because a preservative must saturate the object in 

 lieu of the water. 



Now apply a ten per cent solution of collodion to the ob- 

 ject till the glass is fairly coated with it when it may be 

 dropped bottom side up into eig-hty per cent alcohol to 

 be hardened. This seals up the object and protects it 

 from injury, and it can stay here as loog as desired. 



To stain, haemalum or any other aqueous or alcoholic 

 stain is used. Pass the object (upon the glass) through 

 fifty and thirty per cent alcohol to pure water. Soak in the 

 coloring ag-ent 5 or 6 hours, in water an hour, then back 

 through 30, SO, 75 per cent alcohol. Do not g-o to absolute 

 alcohol unless you wish to dissolve the collodion and re- 

 move the ameba. If the collodion g-ets stained too deeply 

 it must be taken out with alcohol or water. Amylic alcohol 

 does not dissolve collodion and is useful to follow the sev- 

 enty-five per cent alcohol. After quarter of an hour xylol 



