1908] BRIEFER ARTICLES 55 
appearance, but only by comparison with other (especially non-toxic or 
balanced) solutions, or by determination of the freezing-point of the cell 
sap. The protoplasm rounds up just as in true plasmolysis, and may even 
subsequently recover and expand in characteristic fashion when transferred 
to distilled water. 
It may happen that a contraction is caused by true plasmolysis, but the 
subsequent chemical action of the salt renders the protoplasm unable to 
recover and expand when the cell is transferred to distilled water. Such 
recovery cannot therefore be used as a means of distinguishing true plas- 
molysis from a contraction due to chemical action. In some cases the 
contraction may be distinguished from true plasmolysis by the irregular 
outline of the contracted protoplasm. 
On looking over the literature it becomes evident that such precautions 
as are necessary to distinguish this contraction from true plasmolysis have 
not been generally observed in making plasmolytic determinations, and a 
revision of such determinations is necessary. Determination of the freezing- 
Point of the cell sap will certainly be needed in many cases if an accurate 
result is desired. 
In conclusion I would call attention to the importance of this discovery 
in respect to one of the most prominent biological problems, the question 
whether salts are able to penetrate the protoplasm or not. F ar-reaching 
conclusions have been drawn from the fact that when a cell is placed in a 
solution of a certain substance the protoplasm contracts and does not subse- 
quently expand if left in contact with the solution. This has been inter- 
preted to mean that the substance in solution is unable to penetrate the 
protoplasm. I find, however, in many cases, that the true interpretation 
18 exactly the opposite. The permanent contraction of the protoplasm is 
caused by the penetration of the substance in question which produces chemi- 
cal effects upon the protoplasm, wholly different from those produced by 
a substance whose action is purely osmotic. 
In view of this we cannot give credence to certain very important con- 
clusions and theoretical considerations which have been based on this 
criterion of penetrability. These points will receive fuller discussion in a 
subsequent paper.—W. J. V. OsteRHout, University of California. 
* The expression chemical action is here used in a very broad sense to include 
effects which are not osmotic in character. 
