15

2. MOVEMENTS.

     When seen in stools, pus, and in cultures, the amœbæ are actively motile as
a rule. The movement is brought about by the throwing out of pseudopodia.
Often the pseudopodium when first protruded is quite clear and hyaline, but the
coarser granules from the body of the amœbæ rapidly stream into it.

3. MORPHOLOGY.

     (1) Size.—This varies considerably according to the stage of growth of the
animal as will be seen in Plates 1 and 2. The youngest amœba measures three
to four microns (Figures 3 and 4, Plate I), the fully grown amœba being from
thirty to forty microns in diameter, not including the pseudopodia (Figures 1 and
2, Plate I). It is important that this fact should be clearly realised, because in a
stool or in pus from a liver abscess these small forms may predominate, and if
the possibility of their presence is not appreciated a faulty diagonsis as regards
amœbic infection may be given.

     (2) Endoplasm.—This is generally coarsely granular, of greyish and sometimes
greenish tint (Figure 7, Plate I).

     (3) Ectoplasm.—In some cases it is difficult to observe a distinction, but when
the pseudopodia are protruded the ectoplasm will be determined readily as a
clear hyaline strip. it can be seen, also, in the stained preparation (Figure 7,
Plate I).

     (4) Contractile vacuoles.—These were observed in the amœbæ grown on agar,
and, occasionally, in those in the stools. As a rule contractile vacuoles have not
been recorded in parasitic amœbæ, but Noc¹ and Porter² have described
them. They vary in number from one to three or more, they contract suddenly,
once in 15—30 seconds. They appear to have a pinkish tint and are refractile.
The number varies in the same amœbæ at different times.

     (5) Nucleus.—This is excentrically placed at the boundary between the
endoplasm and ectoplasm and is rich in chromatine which stains deeply, and which
is sometimes seen to be surrounded by a clear unstained zone. The changes under-
gone by the nucleus, which are extremely important, will be described below. At
certain stages a clear space is seen in the centre of the chromatine and a nucleolus
may be observed also (Figures 1, 2, Plate I).

     (6) Encystment and reproduction.—These processes require to be studied
with great care as they form a method of classifying the various amœbæ.
Schaudinn is of opinion that the study of the life-cycle of pathogenic protozoa
should precede all experimental researches. To render clear the various

                              ¹Annal. de L'Institut Pasteur, No. 3, Mars 1909.

                              ²Journal of Parasitology, Vol.II 1909.