The detection of distinguishing structural features that may be relied on to separate the species of amebas, especially of the parasitic amebas in the digestive tract of mammals, is fraught with difficulties. These arise from changes in form in the motile phases due to locomotion, to the extrusion and retraction of pseudopodia, to the presence of cytoplasmic inclusions and to the modifications incident on changes in temperature and in hydrogen ion concentration. For example, a slight increase in acidity, as from pH 7.0 to 5.8, markedly increases the locomotor activity and tends to elongate the pseudopodia.
In stained preparations of motile stages, the form of the body and of the pseudopodia is subject to changes due to contraction in smearing and fixation.
In the encysted stages, many of these modifications are eliminated, but others arise which disturb the uniformity of structure. Among these are the volume, number, distribution and time