FEEE-LIVING AMCEBA 15 



should be kept alive as long as possible. In many cases, farther 

 cultivation in small standing aquaria is all that is necessary. But 

 sometimes it will be found expedient to isolate one or more individuals 

 of a species in such a way that they may be kept constantly under 

 observation. For this purpose, Schaudinn's micro-aquarium, 1 the 

 construction of which is quite a simple matter, is very convenient. 



A rectangular piece is cut with an emery-wheel out of one of 

 the long sides of an ordinary glass slide. The excision should measure 

 about 15 mm. by 10 to 14 mm. Over it should be cemented two 

 cover-glasses sufficiently large to cover the opening completely ; the 

 size 21 by 26 mm., usually employed for mounting sections in series, 

 will serve the purpose. The best cement is boiling Canada balsam, 

 such as mineralogists use for mounting transparent sections. As a 

 protective measure, narrow glass strips are cemented on to both 

 surfaces of the slide, close to the two short edges. Water and animal- 

 cules should be introduced by means of a pipette, and the little 

 aquarium may be placed horizontally as, owing to its capillarity, the 

 water will not escape. A twig or two of green seaweed should be 

 put in to keep the water fresh, or, with the micro-aquarium in a 

 vertical position, fresh water may be added by means of a woollen 

 thread from a vessel of water placed at a higher level. By varying 

 the thickness of the glass slide and the size of the excision, the cubic 

 contents of the aquarium can be regulated to suit the requirements 

 of the particular organisms under observation. The micro-aquarium 

 should be kept and studied in a damp chamber. 



The study of Amoebae is greatly facilitated by the fact that they 

 are cultivable upon solid nutrient media. Pure cultures, in a 

 bacteriological sense, are, it is true, impossible ; but Amoebae and 

 bacteria may be cultivated together, the latter serving as food for the 

 former. For this purpose any solid medium may be used, provided 

 that it permits the bacteria a bare existence only, and does not offer 

 conditions so favourable that they are able to overwhelm the Amoebae. 

 Many different media have been used with success, but a formula 

 given by Frosch 2 deserves particular mention : 



Agar-agar 0'5 grm. 



Ordinary alkaline bouillon ... ... ... 1OO ,, 



Tap water ; v. . 90*0 ,, 



Bouillon may be prepared by macerating freshly minced meat in 



1 F. Schaudinn, " Ein Slicroaquarium, welches auch zur Paraffineinbettung 

 kleiner Objekte benutzt werden kann," Zeitschr. f. iviss. Microscopic, vol. xi, 

 1894, pp. 326-329, with one illustration. 



2 P. Frosch, "Zur Frage der Keinziichtung der Amoben," ZentralU. f. Bcikt., 

 part i, vol. xxi, 1897, pp. 926-932. 



