Amebic Dysentery 637 



To isolate and cultivate a single kind of ameba Musgrave and 

 Clegg have recommended an ingenious technic. 



A plate is selected upon which the desired amebas are so widely separated from 

 one another that not more than one is in a microscopic field of a low-power 

 objective. The microscope used should have a double or triple nose-piece. 

 With a low-power (Zeiss A A) objective, a well-isolated organism is brought to the 

 center of the field. The lens is then swung out and a perfectly clean higher-power 

 lens (Zeiss D D) swung in and racked down until it touches the surface of the 

 agar-agar, when it is quickly elevated again. In three out of five cases the ameba 

 adheres to the objective and is so picked up. Whether it has done so or not can 

 be determined by swinging in the low-power lens again and looking for the organ- 

 ism. If it has disappeared, it is attached to the objective. It is now planted 

 upon a fresh plate by depressing the high-power lens until it touches the surface 

 of the culture-medium, when, upon elevating it again, it usually leaves the 

 ameba behind. Observation with the low power will enable one to determine 

 whether it be successfully planted or not. 



Naturally the organisms cannot be thus transplanted without some bacteria 

 falling upon the plate, but this is not very material, for in the first place they do 

 not grow very rapidly upon the medium used for culture, and in the second, they 

 are useful for the nourishment of the ameba, which is holophagous, and cannot 

 live by the absorption of nutritious fluids. 



Later it was shown by Tsugitani* that killed cultures of bacteria 

 could supply the necessary nourishment. All cultures of amebas 

 must contain some kind of cells upon which the amebas can feed. 

 When planted as above suggested a variety of organisms grow, and 

 as the amebas multiply and gradually extend over the plate, their 

 preference for one or other of the associated bacteria may be deter- 

 mined in part by placing a drop of the ameba culture upon a plate 

 of sterile media, and then with the platinum wire, dipped in a 

 culture of the bacteria, and drawing concentric circles about the drop 

 further and further apart. As the amebas move about over the 

 plate, passing through the growing circles of bacteria, they soon 

 lose the miscellaneous bacteria and come to contain the one variety 

 planted with them, or if several have been used in drawing different 

 circles, that one which they prefer to feed upon. By transplanting 

 amebas from plate to plate with suitable bacteria or other cells for 

 them to feed upon, the cultures may be kept growing almost in- 

 definitely. 



Anna Williamsf has been able to grow ameba in pure culture 

 without bacteria, either dead or alive, by smearing the surface of 

 a freshly prepared agar-agar plate with a fragment of freshly re- 

 moved rabbit's or guinea-pig's brain, kidney, or liver, held in a pair 

 of forceps. The ameba gladly take up and live upon the cells left 

 behind upon the surface of the agar. 



Vital Resistance. — 'The free amebas in the intestinal discharges 

 are easily destroyed by dilute germicides and by drying. Encysted 

 amebas are, however, more difficult to kill. They resist drying 

 well and also resist the penetration of germicides. Direct sunlight 

 inhibits the activities of the organisms, but does not kill them. 



* "Centralbl. f. Bakt. u. Parasitenk.," Abt. I, xxiv, 666. 



t "Journal of Medical Research," Dec, 1911, xxv. No. 2, p. 263. 



