176 RESEARCH IN PROTOZOOLOGY 



In order to secure the best results with the two media transfers 

 should be made every twenty-four to forty-eight hours. In these 

 media E. histolytica may be maintained for periods as long as three 

 months but not indefinitely. 



Medium No. 3. N ormal-Salt-Serum Medium. One part of inactivated 

 human blood serum is added to seven parts of normal salt solution (0.85%), 

 filtered through a Berkefeld filter, tubed, and incubated at 2)7° C. to deter- 

 mine sterility. If sterile the tubes are kept in the incubator at this tem- 

 perature until inoculated and incubated at the same temperature. 



In this exceedingly simple medium E. histolytica has been found 

 to grow well for a limited period of time, cultures having been 

 maintained in this laboratory for over two months, transfers 

 being made daily or every two days. It is not as satisfactory a 

 medium for the indefinite maintenance of cultures as the modified 

 Locke-Egg-Serum medium or the Locke-Serum medium. 



Choice of Culture Method. For ordinary diagnostic work, i.e., 

 the demonstration of E. histolytica in the feces, the writer prefers 

 the Locke-Serum medium, although practically as good results 

 are obtained with the Locke-Egg-Serum medium of Boeck and 

 Drbohlav, modified by the omission of dextrose, which is not neces- 

 sary. The addition of rice starch is not necessary in ordinary 

 diagnostic work, but this substance added to either medium in- 

 creases their value if cultures are to be maintained for a long 

 period of time. The simple Normal-Salt-Serum medium has given 

 good results, in diagnostic work, in the hands of several observers, 

 and Vogel (1928) and Kolle and Hetsch (1929) recommend 

 this medium for the cultivation of this parasite. Magath and Ward 

 (1928), at the Mayo Clinic, in a comparison of the Boeck-Drbohlav 

 Locke-Egg-Serum medium and the Normal-Salt-Serum medium, 

 in the cultivation of amoebae from the stools, obtained better re- 

 sults with the latter medium. They obtained eighty-eight positive 

 cultures from 521 stools, or 16.9%, with the Craig Normal- 

 Salt-Serum medium, while with the Boeck and Drbohlav medium 

 they obtained fifty-two positive cultures from 394 stools, or 

 14.7%. Of 115 stools cultured by both methods, the Normal- 

 Salt-Serum medium gave twenty-three positive cultures, or 20%, 

 while the Boeck-Drbohlav medium gave twenty positive cultures, 

 or 17%. 



For the maintenance of cultures by transfer, the writer prefers 

 the Boeck-Drbohlav Locke-Egg-Serum medium, modified by the 



