APPENDIX 417 



tion is autoclaved for 15 minutes under 15 pounds pressure 

 and cooled; then to seven parts of the solution is added one 

 part of inactivated human blood serum. In this culture me- 

 dium, the dysentery amoeba undergoes active multiplication. 

 Some investigators find that N.N.N, medium given above 

 for Trypanosoma is also suitable for intestinal amoebae. 



Plasmodium. — Bass' method is as follows: 10 c.c. of defi- 

 brinated human blood containing Plasmodium and 0.1 c.c. of 

 50 per cent sterile dextrose solution are mixed in test tubes and 

 incubated at 40° C. The cultures are centrifuged to separate 

 the erythrocytes, which sink to the bottom, from the leucocytes, 

 which become collected above. The erythrocytes are now trans- 

 ferred to fresh culture tubes. Several modifications have been 

 made. 



Balantidium coli — Barret and Yarbrough's method is as 

 follows: The medium consists of 16 parts of 0.5 per cent so- 

 dium chloride and 1 part of inactivated human blood serum. 

 It is divided among test tubes. Introduce a small amount of 

 the fecal matter containing the cilitate to the bottom of the 

 tubes and incubate at 37°C. Maximum development is reached 

 in from 48 to 72 hours. Subcultures should be made every 

 second day. Reese used a mixture of 16 parts of Ringer's solu- 

 tion and 1 part of Loffler's dehydrated blood serum. 



Observation 



Protozoa should be studied as much as possible in life. In 

 making fresh preparations care should be exercised to avoid any 

 deformities which might occur owing to the pressure of the 

 coverglass. If small bits of detritus or debris are included in 

 the preparation, the coverglass will be supported by them and 

 the organisms will not receive any mechanical pressure. Al- 

 though ordinary plain slides are used for this purpose, it is 

 often advantageous to use depression slides instead. To make 

 a fresh preparation with a depression slide, the following pro- 

 cedure may be followed: By means of a fine pipette, a small 

 drop of water containing the desired protozoans is placed on 

 a large square coverglass, and is covered with a small circular 

 coverglass, which in turn is covered by a depression slide 

 smeared with vaseline along the edge of the depression, so as 



