12 JOURNAL OF THE [January, 



dated alg^e and infusorians, the bending and distortion of the 

 flexible pseudopods, and the obscuring effect of the common 

 black deposit of reduced osmic oxide. My discovery, on exami- 

 nation of preparations of bacteria by the method already ex- 

 plained, that accidentally I had also successfully mounted some 

 associated amoeboid forms, has resulted in the following process. 

 It has so far been found satisfactory with Amoeba radiosa, small 

 forms of A. princeps, Arcella acuminata, Actinophrys sol, and some 

 amoeboid forms. From present want of proper material I have 

 been unable to determine what modifications may be needed with 

 the larger forms of amoebae, and of other rhizopods with bulky 

 gelatinous material, to prevent distortion by contraction during 

 the drying of the film. 



The thoroughly cleaned thin covers are laid on the bottom of 

 a small Petri dish or similar shallow tray ; to each a large drop 

 of the water containing the living organisms is added, and then 

 set aside in a '' moist chamber," in a quiet, dark, but warm place, 

 for fifteen to sixty minutes. The object is to allow sufficient 

 time for the rhizopods to recover from alarm and to creep about, 

 projecting their pseudopods in a natural way, and yet to prevent 

 any evaporation of the drops. A simple method is to fill a com- 

 mon finger bowl half full of warm water (at 30° to 35° C), to 

 set the shallow dish or tray floating upon the surface of the 

 water, and to cover the whole from the light with a large wet 

 towel folded several times. The vessel is then gently uncovered, 

 without jar, and to each drop a droplet of fixative is added 

 quickly by touching from a drop-tube, but not by dropping, as 

 that would tend to cause tremor in the drop. As fixatives, hydro- 

 gen peroxide, absolute alcohol, chromic acid solution, and, per- 

 haps best of all, osmic acid solution (i per cent), were" used. The 

 tray is then removed from the "moist chamber," the drops are 

 allowed to evaporate, as in the process for preparations of bac- 

 teria, and the films treated as before explained. 



Also, to a drop of water containing rhizopods under observa- 

 tion, on the stage of a microscope (an inverted stand is prefer- 

 able), under a half-inch objective, the droplet of fixative may be 

 directly applied at the proper moment of the projection of the 

 pseudopods, and the evaporation, etc., then carried on as already 

 described. 



