288 Seifriz. — Observations on some Physical Properties of 
4. The plasma-membrane is commonly of high viscosity, undoubtedly 
a gel, but it readily reverts to the liquid sol state. 
5. The plasma-membrane is, above all, facile. It is capable of ready 
adjustment to changes in contour and area. 
6 . One of the characteristic properties of the living substance is the | 
capacity to form, almost instantly, a membrane on its surface. The few | 
apparent exceptions to this have to do with protoplasm of extreme 
liquidity. 
7. The living membrane, though rather sharply delimited from the 
inner plasm, is not capable of isolation. 
8. The degenerate, coagulated plasma-membrane can sometimes be 
isolated. It is then seen to be of very firm consistency, elastic, and 
exceedingly tough. 
9. The nucleus and vacuoles also possess protoplasmic membranes 
which are closely similar to the outer plasma-membrane. 
10. The thickness of the plasma-membrane is probably about o*i [x. 
II. THE NON-MISCIBILITY OF PROTOPLASM IN WATER. 
If we accept a simple, non-technical definition of the term miscibility 
we may then proceed with satisfaction to a discussion of the problem of the 
miscibility of protoplasm in water. If, however, we try to base our defini- 
tion on the molecular physics of the phenomenon we are likely to get into 
difficulty, because our problem will become so involved with the physics of 
diffusion and imbibition that the original simple question, Is protoplasm 
miscible in water ? will be completely obscured in a theoretical discussion. In 
order, however, to arrive at a definition of miscibility which will avoid danger | 
of confusing the latter with the closely related phenomenon of imbibition it 
will be necessary to discover to what extent one is justified in distinguishing 
between the two phenomena. 
When a dry reversible gel, such as glue, is wetted, there is first a pro- 
nounced swelling, but the individuality of the original piece of glue is not 
lost. The piece has merely increased in volume. So far, only imbibition, 
i.e. absorption of water and consequent swelling, has taken place. But as 
absorption increases the original glue mass begins to disintegrate, and 
ultimately we have an aqueous dispersion (colloidal solution) of glue. 
Imbibition has given way to diffusion, and the merging of the one 
phenomenon into the other was gradual and imperceptible. In the last 
analysis the molecular physics may be the same in both cases, the distinction 
between the two phenomena being merely one of degree. 
It is quite possible that the behaviour of protoplasm in relation to 
water is closely analogous to that of glue, and we are thus put to it to 
decide whether the taking up of water by protoplasm is to be regarded as 
