540 CLASSIFICATION AND MORPHOLOGY OF AMEBA 



found in the intestines of a great variety of animals, where they lead 

 a parasitic, but as a rule perfectly harmless, life. 



Microscopic Study. The study of ameba is to be undertaken on 

 fresh preparations in the live state, and it is then best to use the fluid 

 in which they naturally occur. Saprophytic amebae are, therefore, 

 best studied in the water in which they are found; parasitic amebse 

 can be studied in feces or in scrapings from the intestines, perhaps 

 mixed with a small amount of physiologic salt solution. Of such 

 fluids containing saprophytic or parasitic amebse a hanging drop may 

 be made or a drop of the fluid is placed on a slide and covered with 

 a cover-glass. If the cover-glass be used it is well to supply it with 

 four very short wax feet, so that the weight of the cover does not 

 compress the amebse, as they are much more sensitive to insults 

 than bacteria, and a small degree of pressure may injure them. When 

 amebse in semisolid or semifluid feces are studied it is not necessary 

 to supply the cover-glass with wax feet, because such material generally 

 contains a sufficient number of undigested particles to furnish a 

 support for the cover-slip. When parasitic intestinal amebse are 

 studied in the fresh state it is well to warm the slide and cover-glass, 

 because such amebse lose their motility as soon as they are materially 

 cooled. Care should be taken not to heat the slide and cover-glass 

 too much, as otherwise the amebse go into a condition of "heat rigor," 

 and become likewise immobile. The best method of warming the 

 slide and cover-slip properly is to immerse them for some time in 

 water a little warmer than body temperature (about 40 C.). 



Staining Properties. Amebse should also be studied in stained 

 preparations. The simplest method of studying stained amebse 

 consists in the preparation of thin smears or spreads on cover-glasses. 

 For the study of intestinal amebae, Craig recommends Oliver's 

 modification of Wright's staining method. The spread is made on 

 the slide and is allowed to become air dry, and then a few drops of 

 Wright's stain are poured on the slide. The stain, being dissolved 

 in methyl alcohol, fixes at the same time that it dyes. The stain 

 is allowed to act for five minutes, then enough distilled water is 

 added to cause a slight metallic scum to appear on the surface. The 

 dilute stain then remains on the slide for ten minutes longer and 

 the preparation is finally well washed in distilled water and dried 

 between filter paper. The slide is not mounted in Canada balsam, 

 but is examined directly with the oil-immersion lens. If after exam- 

 ination the specimen is to be preserved the immersion oil is washed off 

 with xylol. Walker recommends the chloride of iron hematoxylin 

 method of Mallory for staining amebse in slide and cover-glass 

 preparations. The smears after being air dry must first be fixed 

 a short time in Zenker's solution, 1 then washed successively in water, 



1 Zenker's solution is composed of bichloride of mercury, 5 grams; bichromate of potash, 

 2.5 grams; sulphate of sodium, 1 gram; glacial acetic acid, 5 c.c.; and water enough to make 

 100 c.c. 



