AMCEBINA 17 



form more or less numerous finger-shaped pseudopodia ; others again, 

 especially A. verrucosa, adopt a more or less distinct rolling movement. 1 

 The movements of Amoebse are influenced, moreover, by the medium 

 in which the organisms are examined. On a colloid nutrient medium, 

 for instance, they are slower than in water. The separation of the 

 endo- from the ectosarc should be carefully noted, and the behaviour 

 of both plasma during movement, as well as the regular action of the 

 contractile vacuole, should be observed. Under favourable conditions 

 it is sometimes possible to watch the ingestion of food particles by the 

 process of "enfolding" and " drawing-in," as also the rejection of 

 undigested food remnants. The nucleus, however, can as a general 

 rule be studied in fixed and coloured specimens only. 



The process of preserving Amoebae can generally be carried out on 

 the cover-glass. This is rarely possible, however, in the case of the 

 soil Amoebse, the superficial layer being here, as in the Infusoria, 

 thickened into a close pellicle which prevents the organism adhering 

 to the cover-glass. In the case of other species, a portion of the 

 material containing the organisms (scum from straw or hay infusions 

 should be triturated) should be transferred to a cover-glass, which is 

 placed for ten minutes in a damp chamber. The cover-glass is then 

 dropped, material downwards, into a small vessel containing hot 

 alcoholic solution of sublimate. The cover-glass may now be rinsed, 

 when it will be found that all extraneous matter and foreign organisms 

 are washed away, while the Amoebae remain upon the surface of the 

 glass. This is explained by the fact that, during progression, Amoebae 

 secrete a sticky substance, which causes those individuals who have 

 changed their position upon the surface of the glass, to adhere to it- 

 Cover-glass preparations may similarly be made from Amoebae culti- 

 vated upon solid media, by laying a cover-glass upon the surface of 

 the medium, pressing it well down, and leaving it for several minutes. 

 Preparations coloured with diluted haematoxylin, borax- or alum- 

 carmine, or iron-haematoxylin, show with singular clearness the 

 structure of the nucleus. In appearance it resembles a bubble, and 

 it invariably contains a caryosome, which stains a darker colour than 

 its surroundings. In many species, A. Umax for instance, this 

 caryosome is so large that a superficial observer might easily mistake 

 it for the nucleus itself. 



The study of the nucleus and the cysts, however, demands the 

 preparation of sections. These are best prepared from agar cultures, 



1 A detailed description of the movements of different Amoebae is given in 

 H. S. Jennings' " Contribution to the Study of the Behaviour of Lower Organisms," 

 Washington, 1904 ; also L. Rhumbler, " Zur Theorie der Oberflachenkrafte der 

 Amoben," Zeitschr.f. miss. Zool., vol. Ixxxiii, 1905, pp. 1-52. 



2 



