JANUARY 19, 1912] 
the increase of resistance which is observed 
when the tissue is transferred from NaCl + 
CaCl, to pure CaCl, of the same conductivity. 
On one hypothesis the plasma membrane 
would retain its normal properties after the 
transfer but would show increased resistance 
because it is normally less permeable to the 
ions of CaCl, than to the ions of NaCl. 
On the other hypothesis the plasma mem- 
brane would suffer a change in its properties 
as the result of the transfer. The facts 
strongly favor this hypothesis. I will men- 
tion only afew. Visible changes in the outer 
layer of the protoplasm are produced by CaCl, 
(and many other substances) and this makes 
it probable that the plasma membrane suffers 
change. Alum, which is known to alter the 
properties of many colloids (e. g., in tanning), 
when added in solid form to the sea water 
greatly increases the resistance of the proto- 
plasm although it greatly decreases the resist- 
ance of the sea water. In this case the only 
explanation is that the permeability of the 
plasma membrane is altered. On the other 
hand it is clear that the large number of sub- 
stances which produce irreversible decrease of 
resistance must also alter the plasma mem- 
brane. 
It seems probable therefore that a great 
variety of substances alter the plasma mem- 
brane so as to increase or decrease its per- 
meability. 
It may be pointed out that these results are 
precisely what should be expected if the an- 
tagonistie action of salts is due, as Loeb has 
suggested, to the fact that they hinder each 
other from penetrating the protoplasm. It is 
quite clear from the experiments that CaCl.,, 
SrCl, and BaCl, in small amounts are able 
to hinder very greatly the entrance of the 
ions of NaCl. The mechanism of this action 
is not fully understood, but I may state that 
CaCl,, BaCl, and SrCl, bring about visible 
changes in the plasma membrane which are 
entirely different from those produced by such 
salts as NaCl. It is hoped that a further 
study of these visible changes may throw light 
on this question. 
Previous experiments on plasmolysis have 
SCIENCE 
115 
shown essentially similar phenomena and the 
complete confirmation of the results of one 
method by those of the other form the most 
striking proof possible of the facts outlined 
above. 
It may be asked how merely delaying the 
entrance of a salt can protect the protoplasm 
against its toxic action. In this connection 
it may be pertinent to recall the familiar phe- 
nomenon of colloid chemistry that a salt which 
produces marked effects when added suddenly 
may produce little or no effect when added 
slowly. It should be noted that there is good 
evidence to show that the NaCl does not enter 
the cell alone but is accompanied by CaCl,. 
It is possible that these salts may wholly pre- 
vent each other from penetrating internal 
membranes (e. g., the nuclear membrane) 
which are of importance in this connection. 
The chief conclusions are as follows: 
1. Quantitative studies of permeability may 
be made by a simple and accurate method. 
2. Slight changes in the rate of penetration 
may be observed and accurately measured at 
very brief intervals. 
3. A great variety of anions and kations 
readily penetrate living protoplasm. 
4. Inasmuch as these ions are insoluble in 
lipoid it would appear that Overton’s theory 
of permeability can not be correct. 
5. The plasma membrane is readily altered 
by a variety of substances in a fashion which 
is easily understood on the hypothesis of a 
colloid (probably proteid) plasma membrane 
but which can not be explained on the hypoth- 
esis that the plasma membrane is a lipoid. 
6. The antagonistic action of salts is largely 
or entirely due to the fact that they hinder or 
prevent one another from entering the pro- 
toplasm. 
W. J. V. OsTerHOUT 
LABORATORY OF PLANT PHYSIOLOGY, 
HARVARD UNIVERSITY 
NOTES ON THE DISTRIBUTION OF THE SOUTH- 
EASTERN SALAMANDERS (GEOMYS TUZA AND 
ALLIES) 
A cuaracteristic feature of many parts of 
the pine forests of the coastal plain of Georgia, 
