Protoplasm by Aid of Microdissection . 277 
These observations support the theory of amoeboid movement advocated 
by Hyman, who says (21, p. 88) : ‘ Since the ectoplasm is a more or less 
rigid gel, the direct cause of pseudopod formation must be a local liquefac- 
tion, and the direct cause of the withdrawal and contraction of pseudopodia 
must be coagulation. This gelation and solation are the essential processes 
in amoeboid movement.’ I believe, however, that it is probably primarily 
the membrane which functions in this solation-gelation phenomenon, since it 
becomes much firmer on gelling than does the ectoplasm. 
A further bit of experimental evidence tending to show that the surface 
of protoplasm is far more viscous, resistant, and elastic than the interior, is 
to be had by tearing apart a mass of inactive and very viscous protoplasm. 
If two needles are placed within the highly viscous protoplasm of a myxo- 
mycete plasmodium and are then separated, the protoplasm will, as the limit 
of extensibility is approached, tear very much as bread-dough does when 
pulled apart, but there is almost invariably a remaining strand which persists 
for some time after the mass as a whole has separated. This remaining 
strand may be stretched to a very fine thread, exhibiting a surprisingly high 
extensibility. This persistent thread of protoplasm is always from the 
surface of the torn mass. If, now, the one needle is returned and again 
put into the protoplasmic mass near the ragged surface from which the 
membrane just described has been torn (the highly viscous and partly 
degenerate condition of the protoplasm prevents the formation of another 
membrane, i. e. the wound is not healed) and the two needles are again 
separated, the mass of protoplasm, when its limit of extensibility is reached, 
tears apart abruptly and cleanly. There is now no persistent outer layer of 
more viscous, resistant, and elastic protoplasm. 
One of the fundamental properties of the living substance is the 
capacity instantly to surround itself with a membrane such as that which has 
just been described. Tears in the plasma-membrane are usually instantly 
repaired. When the surface of a plasmodium or of an Amoeba or an ovum 
is torn, it is, if the protoplasm is normal, immediately healed, and there 
is seldom any escape of protoplasm. This capacity exists even in the ova 
of Fucus , where the outer layer is not a membrane but a pliable wall of con- 
siderable thickness. A tear in this wall is rapidly repaired, the new covering 
being to all appearance identical with the old.' 
This capacity for forming protective membranes is to be observed 
in the behaviour of escaped masses of protoplasm. For example, ejected 
masses of protoplasm from pollen tubes sometimes develop membranes imme- 
diately on being freed. (The behaviour of escaped protoplasm from growing 
pollen tubes varies greatly. It is sometimes immiscible in the surround- 
ing medium of water and immediately forms a membrane on being freed, 
while it equally often diffuses rapidly into the water with no indication 
of the formation of a membrane.) The membrane formed is surprisingly 
