276 Seifriz — Observations on some Physical Properties of 
surface layer is exceedingly delicate, of immeasurable thickness, and is not 
identical with the hyaloplasmic border (or ectoplasm), which, to be sure, it 
resembles in constitution, but from which it is more or less sharply 
delimited . 1 
The following extract from notes on my experiments shows how 
closely the behaviour of the surface layer of Amoeba resembles that of 
myxomycete plasmodia, and, like the latter, supports the theory of a delicate 
protoplasmic membrane. 
4 That portion of the membrane of new pseudopodia of Amoeba which is 
immediately concerned in the advancement of the pseudopodia— that is, the 
region of the membrane at the foremost tip of an advancing pseudopodium — 
is in a state of fluidity, while those regions of the membrane bordering the 
more or less quiet portions of the Amoeba are of very high consistency, 
undoubtedly a colloidal gel. The rapidity with which the liquid membrane 
of an advancing pseudopodium will gel is beautifully seen in the result 
of a rapid stretching of it. If the membrane of a quiescent Amoeba is torn 
it is found to have the consistency of a gel, and, though elastic, it tolerates 
only a moderate amount of stretching. On the other hand, the liquid 
membrane bounding the advancing part of a moving Amoeba behaves 
at first, if the dissection be quickly performed, exactly like the liquid 
membrane of a water droplet, but extension of the liquid membrane is 
possible for only a brief space of time, for gelation quickly takes place, 
after which the now gelled membrane may be stretched a bit, when it 
breaks. 
The behaviour of the ectoplast is quite similar to that of the membrane, 
in this respect differing markedly from the hyaloplasmic border of myxo- 
mycetes. The ectoplasm of Amoeba is in a liquid state when actively 
flowing, but when quiet is of high consistency, though it never attains 
the rigidity of the passive membrane. It is this difference in density and 
consequent difference in degree of extensibility which makes it possible 
often to distinguish the membrane from the ectosarc even in the living 
condition. 
The resistant, elastic, and highly viscous gel nature of the surface layer 
of Amoeba is evident from the following experiment. An active specimen 
of Amoeba was twice partially severed, leaving but a strand (apparently 
double) of protoplasm, the plasma-membrane, connecting the two halves. 
Subsequently, after the needles were removed, the two halves were drawn 
towards one another by contraction of the connecting elastic gel membrane, 
and on coming in contact they re-joined,’ 
1 De Bary’s notion of the plasmodial membrane was also essentially this. He says (3, p. 42) : 
‘ These facts ... do not permit it (the plasma-membrane) to be considered as a skin differentiated 
from the ground-substance, but it is to be looked upon as a special superficial layer of the living 1 
plasmodium, from which it is usually readily distinguishable.’ 
