566 MARY J. HOGUE 



MATERIAL 



The material used for these experiments came from a pure line 

 of a limax amoeba. This amoeba had been isolated and the 

 pure line started nearly a year ago. Since then it has been grow- 

 ing on agar-agar made up with tap water and Witte's peptone. 



It may be interesting to note the method of isolation used. 

 The amoebae were allowed to spread out on the agar in the Petri 

 dishes until those at the edge were afar apart from one another. 

 Then small blocks of agar containing one amoeba were cut out and 

 placed on fresh culture dishes. 



The amoebae were studied in media of six different densities; 

 water, and agar-agar of 0.5, 1, 1.5, 2, and 2.5per cent. To these 

 different preparations of agar, which had been made up with tap 

 water, 0.4 per cent of Witte's peptone was added and the media 

 were then sterilized in the autoclave for twenty minutes under 

 fifteen pounds of pressure. The precaution was taken ;that all 

 the media should be cooked the same length of time and should 

 in every respect be treated exactly alike so that the relative 

 densities would be the same. 



Wherry's ('13) medium of water, egg albumen, and the yolk 

 of the hen's egg was made up in the different percentages of agar. 

 Unfortunately the bacteria on which the amoebae live multi- 

 plied so rapidly here, that the amoebae were soon exterminated, 

 though at first they had been unusually large. 



The agar of 0.5, 1, 1.5, 2, and 2.5 per cent was poured out 

 into sterile Petri dishes. Agar of 0.5 per cent was also poured 

 upon depression slides, as it was often impossible in warm weather 

 to invert the Petri dish containing the thin agar. These shdes 

 were kept in moist chambers. The amoebae were transplanted 

 from old cultures by means of the platinum loop. 



In order to make camera drawings pieces of agar containing 

 the amoebae were cut out and put on a slide. In this way a 

 much higher magnification could be obtained than with the in- 

 verted Petri dishes. For the drawing of amoebae on 0.5 per 

 cent agar those grown on the depression slides had to be used as 

 it was impossible to cut blocks from this soft medium. 



