No. 633] FREE-SWIMMING MASTIGOPHOBA 337 



agitated before adding to the culture drop. This in- 

 cludes numerous minute air bubbles, around which the 

 animals may gather and so become concentrated, if the 

 solution is at first thin enough to allow them to make 

 their way through it. It was' found that gelatine that 

 had stood ready made up for some time in a warm room 

 became cloudy in appearance and stringy in texture, due 

 to the growth of mould plants and colonies of bacteria. 



Another method of retarding the motions of the flagel- 

 lates, which was partially successful with such minute 

 forms as Plcuroinojuis jaciihnis and FA r ire a cionur, was 

 to chill the slide and its water drop thoroughly on a block 

 of ice. This was tried in midsummer, when the sudden 

 reduction in temperature of water that had been quite 

 warm (the culture having stood in the sun) apparently 

 paralyzed the organisms, but they regained their wonted 

 activity after a few minutes' time, since the slide could 

 not very conveniently be kept chilled under the micro- 

 scope. 



The favorite method of the writer for quieting without 

 killing was to utilize a minute aquarium, of a sort that 

 might be used even under the high powers. This was 

 constructed by cutting out a circle of very thin typewriter 

 manifolding paper of good grade and firm texture of 

 slightly less diameter than that of the cover glass, and 

 then cutting from the center of this a concentric aperture 

 about 5 mm. in diameter. This was affixed to the slide 

 with a ring of thin balsam or castor oil, applied with a 

 fine earners hair brush; the water drop placed in the cen- 

 ter, and the cover glass, also ringed with thin balsam or 

 oil, carefully lowered thereon. The oil or balsam sealed 

 the cover glass, and the paper kept it from descending 

 far enough to crush the incarcerated organisms. 



At first the flagellates in such an aquarium swim about 

 at their normal rates of speed, but after a time they be- 

 come stupefied, probably because of the gradual exhaus- 

 tion of the oxygen supply, and their movements become 



