919 
In general appearance it is usually somewhat more dense than the 
endoplasm, particularly on its outer border; it may appear as a homo- 
genous structure, or again may present a granular appearance without 
color, or may be of a grayish or greenish tint. Its association with the 
internal parts of the amoeba may be so close that no line of demarcation 
can be made out, or again it may stand out with perfect clearness, entirely 
separated from the endoplasm. 
In young ameebe of whatever species the distinction between ectoplasm 
and endoplasm is rarely demonstrable, and even in adult types or 
in encysted forms this may be very difficult. In old, encysted amcebe 
the density of the ectoplasm appears to increase and its contraction 
causes a wavy appearance which, together with the slight, brownish color 
which may also be present, may with age give a picture comparable with 
that seen in ascaris eggs. (Fig. 29, in Publications of the Bureau of 
Government Laboratories, Biological Laboratory No. 18.) At times, it 
may seem perfectly structureless, or thicker and denser on the outer 
margin, shading off toward the center of the parasite, or in some 
instances it seems to have a sharp, well-defined inner membrane as well as 
an exterior one. Often, particularly in this latter type, it contains a few 
or many granules of assorted sizes, distributed in its substance. 
This part of the amceba is probably a much more complex structure, 
both histologically and functionally, than it is generally accredited to be. 
Numerous observations tend to show the correctness of this conclusion. 
At times, during the vegetative stage of the amoeba, it allows the 
passage into and out of the parasite, of bacteria, red blood corpuscles,* 
and of other foreign, formed elements of considerable size, and again, 
during the encysted stage of the organism, it proves to be almost, or 
quite, impervious to the most powerful staining reagents. 
It is a fact that no satisfactory staining reagent for encysted amabx 
has been found. The ectoplasm may be most intensely stained by almost 
any common dye, but there is very little penetration to the interior 
structures. On the contrary, this is not true in the vegetative stage, 
and an almost equally large number of stains may be used, which will 
even color the interior structures more intensely than they will the 
ectoplasm. ‘This,’in our opinion, depends more upon variations in the 
ectoplasm than upon changes in the other structures of the parasite 
with reference to susceptibility to stains. 
Further corroboration of this fact is found by a study of the action of 
dilute solutions of neutral red upon ameebee. Solutions of this substance, 
so dilute that the color in a drop can scarcely be detected by the eye, when 
*We must not forget here that it is possible that these bodies never actually 
penetrate the ectosare, but that folds of this membrane envelop them, so that 
they are only apparently in the ameebe, in a manner comparable to the relation 
between the peritoneum and the abdominal organs. 
