114 E. PENARD ON THE COLLECTION AND PRESERVATION OF 



Second Method. 



Suppose that in a gathering I have noticed an abundance of 

 a certain species — say Difflugia ]yy r ifomiis — which I wish to 

 mount in great numbers. 



After having put some parcels of the gathering in a large 

 flat-bottomed capsule (such as a cover of one of those glass boxes 

 that are supplied by all dealers in microscopical apparatus), I 

 take the animals in a pipette one after the other under the 

 simple microscope, and I transfer them, with such impurities as 

 may accompany them, into another flat-bottomed capsule filled 

 with clean water. After a moment I take these specimens 

 again under the simple microscope, and transfer them to a 

 watch-glass, where this time the impurities are in a negligible 

 quantity.* 



From this watch-glass I remove the greater part of the liquid, 

 only leaving my Difflagiae with just suflicient water to enable 

 them to spread out their pseuclopodia freely. I allow the glass 

 to rest for about a quarter of an hour, and then suddenly, from 

 a well -filled pipette, I drench all with a jet of absolute alcohol, 

 taking care that the stream of alcohol is abundant, and makes a 

 circle round the liquid which covers the bottom of the watch-glass, 

 for without this precaution the specimens are often thrown to 

 the side on to the dry glass, where the plasma shrivels up 

 immediately. 



After some minutes I withdraw a part of the alcohol and 

 replace it with borax carmine, which I allow to act for some 

 time — for a quarter of an hour to an hour, according to the 

 strength of the reagent. f 



* To avoid the risk of losing individual specimens during these transfers, 

 it is necessary to fill the pipette gently and only half full. If it is allowed 

 to fill rapidly and right up, it generally produces a whirl which draws the 

 object to the surface of the water that is sucked up. The object imme- 

 diately gains the edge of the concave surface of the water, and fixes itself 

 to the glass, from which it is removed with difficulty. 



f The strength of the carmine depends on the way in which it has been 

 prepared. Certain rhizopods, however, colour more quickly than others ; 

 and in all, if it is wished to colour the pseudopodia sufficiently, the 

 nucleus must be sacrificed more or less, as it will be too deeply coloured, 

 only showing a large spot of dark red, the nucleoli not being distinguish- 

 able from the rest of the nuclear mass. 



