Protoplasm by Aid of Microdissection . 275 
and therefore is of low viscosity, is pierced by a microdissection needle and 
the needle is slowly moved toward the edge of the protoplasmic mass, the 
liquid hyaloplasm will follow the needle until a good-sized artificial pseudo- 
podium is produced. The formation of so large a pseudopodium necessitates 
considerable increase in surface of the plasmodium in that region, to 
accomplish which the outer layer must either be in a liquid state or, if solid 
(i. e. a gel), must be capable of being greatly stretched. That the membrane 
is not elastic is readily determined when such a pseudopodium is being 
formed by releasing the needle and observing the absence of any appreci- 
able contraction. The outer layer, therefore, must during pseudopodium 
formation, be in a liquid state. Increase in surface is accomplished by 
additions to the outer layer from the liquid hyaloplasm. There is no 
stretching in the sense of an elastic membrane, no great separation of the 
surface particles, but, as in any liquid film, with increase in area more 
pa v ticles are forced into the surface layer. 
The experiment so far has proved only that the plasmodial surface is 
at pseudopodium formation liquid ; but that it differs from any other liquid 
surface has not been shown. Optically the liquid surface layer of a plas- 
modium is much more refractive in comparison to the interior protoplasm 
than is, for example, the liquid surface of water dn comparison to its 
interior. In observing these liquid surfaces of streaming protoplasm one 
constantly gets the optical impression that the outer layer differs, and is 
sharply delimited from the bordering hyaloplasm. 
The advance of such an artificially produced pseudopodium will at 
some point suddenly be halted by a change in consistency of the protoplasm, 
and this pronounced and sudden change takes place at the surface , for the 
inner hyaloplasm increases but little in viscosity. Subsequent advance- 
ment of the needle causes a break in the surface. The break is not sudden, 
however, for there is now some actual stretching of the firm (gelated) 
surface layer, which ultimately tears apart. 
From these observations we may justly conclude that the surface layer 
of an advancing myxomycete pseudopodium is liquid, while that of an 
inactive one is firm. When a quiescent, and therefore more viscous, 
plasmodium is dissected in the manner above described there is no flow of 
protoplasm. The surface layer is, after some stretching, ruptured. We 
have here then a reversible solation-gelation phenomenon. The inactive 
surface layer is a highly viscous emulsion colloid, undoubtedly in the gel 
state , 1 which solates (i. e. becomes a sol) when streaming takes place, and 
reverts to the gel state when the plasmodium again becomes inactive. This 
1 The only criterion here for a gel or sol state is viscosity. This does not furnish conclusive 
evidence, but where the viscosity is so very high or so very low one can be reasonably certain that 
the protoplasm is, in colloidal structure, actually a gel in the first case, or a sol in the second case, 
(For a more complete discussion of this see 38.) 
T % 
