PATHOGENIC PROTOZOA. 413 



Other species from wandering in. After isolation by method 

 just described the cell is allowed to multiply where it is, and 

 after it has done so, as shown by observation with the micro- 

 scope, further culture may be made on fresh tubes or plates. 

 These cultures are pure only in the sense that they contain 

 only one kind of ameba, but they require the presence of 

 bacteria for growth as has been elsewhere stated. 



Study of the Ameba on Cover-glasses. — Hill's hanging 

 block method is not well suited to the purpose of studying 

 the amebse for the reason that these grow only upon the 

 surface but agar spred in a thin film on a cover-glass answers 

 the purpose well. The method of procedure is to spread the 

 melted agar on the cover-glass, and protect it against contami- 

 nation from the air by placing it under a flamed watch glass. 

 The spreading is affected with a large platinum loop. The 

 agar is inoculated with the ameba, and the cover-glass onto 

 which it is attached is placed on a hollow slide in the manner 

 used in making the usual hanging drop cultures of bacteria. 

 After the vaseline is streaked around the hollow in the slide, 

 the latter may be pressed down over Ihe cover-glass containing 

 the inoculated culture mediuiji, or the cover-glass may be 

 turned over on to the slide in the usual way. 



Reproduction in the Genus Ameba. — Studied in the 

 "hanging plate" method just described, ameba are seen to 

 pass through several stages. The ameboid stage may give 

 rise to other ameboid forms by division, or to a resting stage 

 through encystment, or finally to the production of young 

 amebae through spore formation. 



In the process of development first mentioned the cell comes 

 to rest, becomes rounded and then oval, and finally becomes 

 constricted into a mother and a daughter cell by transverse 

 division. Sometimes the two cells remain attached by a 

 thin thread of protoplasm which stretches to several times the 

 diameter of the cells. The cells are sometimes pulled together 



