530 APPENDIX 



dead, though still green, water plants in the bottom of a 4 by 6-inch 

 battery jar which has been carefully sterilized, and pour on aerated 

 distilled water to a depth of 2^ to 3 inches. It is v.ery important not 

 to use too much plant material. In general, sufficient weed material 

 should be added to cover the bottom with a greenish layer. In addi- 

 tion, place in each culture 8 or 10 wheat grains which have been thor- 

 oughly boiled. After the culture has stood for one week, add a pure 

 culture of amoebas. If you have no amoebas, look for them in their 

 natural habitat, e.g., pond or aquarium. Only a-very small variety 

 of amoebas are usually found in such places. If a greater variety is 

 preferred, they may be purchased from a biological supply house. ^ 

 By re-culturing from time to time amoebas can be kept for the entire 

 school vear. 



The amoeba culture should be kept in medium light and in a cool 

 room where the temperature does not vary greatly. An optimum 

 of 20° C. (68° F.) is satisfactory. It is difficult to keep amoeba cultures 

 during the summer because of the high temperature. However, if 

 the cultures are stored in a cool, fairly well-lighted basement, the 

 animals will usually survive. 



Upon the bottom of the properly prepared amoeba culture, there 

 forms a greenish layer of loose material. Microscopic examination 

 will show that this layer is rich in diatoms, desmids, and other plant 

 cells and it is on and in this bottom layer of greenish material that the 

 amoebas feed and multiply. Within a week or, at most, two weeks 

 after inoculation the culture should be rich in amoebas which will 

 generally live and reproduce for some time. 



The main point to be emphasized in connection with this type of 

 culture is that the water must remain clear. That is, it should not 

 become cloudy or show evidence of fermentation in the formation of a 

 surface film or scum. If the culture develops either of these charac- 

 teristics, too much plant material is present and such a culture should 

 be thrown out and a new one started. 



1 Satisfactory cultures of Paramecia and amoebas may be obtamed either 

 from the New York Biological Supply House or J. D. Dawson, College of 

 the City of New York, New York. 



