T. G 00 DF.Y AND A. W. Weldings 
5:39 
In making cover-slip preparations we have taken a small quantity 
of material from the mouth, whether pyorrhoea pus or food or other 
debris by means of a sterile needle or capillary pipette and have teased 
it up with a platinum loopful of a diluting solution. 
The solutions used for this purpose have been normal salt solution, 
saliva, salt-citrate solution of the strength recommended by Minchin^ 
for the examination of trypanosomes, and salt-citrate solution to 
which 15 % white of egg has been added. By the use of the last- 
mentioned solution it is. possible to get very good film preparations on 
fixation, for the egg-albumen in coagulating adheres to the cover-slip 
and holds most of the bodies present in the film. 
It is important in making hanging-drop preparations to use only 
the minimal quantity of diluting solution, so as to ensure a thin layer 
of liquid when the majority of the leucocytes and organisms will be 
found on the glass surface, and not on the lower surface of the drop. 
If too much solution is taken, not only is it very often impossible to use 
high powers in the examination of the organisms, for most of the latter 
gravitate to the lower surface of the liquid, but when the cover-slip is 
lifted, and dropped on to the fixative*, all those bodies on the lower 
surface of the drop are washed off and are lost. We have found normal 
salt solution and salt-citrate solution with or without egg-albumen 
equally good as the diluting solution. 
(b) Fixed and stained material. 
As fixatives we have used Maier’s solution which is very similar to 
Schaudinn’s sublimate alcohol, Bonin’s fluid, and absolute alcohol. 
The last is especially useful for rapid work when methyl-green is 
used as the subsequent stain. Maier’s and Bouin’s solutions appear to 
give equally good results but we have used Maier’s solution most 
frequently. 
After fixing we have followed the usual procedure for the manipu¬ 
lation of wet films, washing out the fixative and finally bringing the 
preparation into the desired staining solution. It may not be out of 
place at this point to call attention to the utter uselessness of dry-film 
preparations for the exact cytological study of mouth amoebae or of 
any other protozoa. We have seen particulars given for the making 
of such dry-films by the usual rapid bacteriological methods and 
recommending the use of certain rapid stains such as thionin-blue. 
^ 1 grm, sodium citrate and 1 grm. sodium chloride dissolved in 200 c.c. distilled water. 
