502 
Seifriz.—Observations o?i the Reaction of 
The term plasma membrane is here employed to mean that part of the 
cell which is concerned in the phenomena of permeability without neces¬ 
sarily implying that all permeability phenomena are traceable to the 
activities of a morphologically definite membrane on the surface of proto¬ 
plasm. That the surface layer of the protoplast is not the only region 
which is concerned in permeability changes is evident from the following 
observed phenomenon. 
The layer of protoplasm lining the wall of a normal Elodea cell is 
relatively thin. In saponin-treated cells this protoplasmic layer may 
become increased to five times its normal thickness through excessive 
imbibition of water due to highly increased permeability of the protoplast 
as a whole} 
Protoplasmic Streaming. Streaming of protoplasm is greatly stimulated 
by the saponins. The number of cells exhibiting streaming, the rate, and 
the abnormal types are exceedingly great.- 
Discussion. 
The similarity in the reaction of protoplasm to two such widely 
differing substances as alcohol and saponin is most striking. It will be of 
interest to consider how far existing theories of permeability go towards 
explaining the effect of alcohol and saponin on protoplasm. 
Overton ( 19 ), in his classical work on the osmotic properties of the cell, 
found that those alcohols which are most toxic to the living cell are also the 
alcohols which most readily attack lipoids. He therefore concluded that 
the chief constituents of the plasma membrane were lipoids. This lipoid 
theory of Overton was widely accepted at the time (1901) and prevailed 
until Traube ( 24 ) twelve years later advanced the hypothesis that a sub¬ 
stance entered a cell in proportion to its capacity to lower surface tension ; 
and the more rapidly it entered, the more toxic was its influence. Con¬ 
sequently, ‘ isocapillary ’ solutions of different narcotics produce the same 
end result because the same quantity enters in the same length of time. 
Following Traube’s surface-tension conceptions came the theory of 
Czapek (6). According to Czapek, water-soluble and surface-tension active 
substances begin to effect exosmosis of the contents of plant cells when of 
a concentration with the tension value of 0-685, which Czapek believed to 
1 One may here refer briefly to the bearing of this excessive imbibition of the protoplast as 
a whole on the structure of protoplasm. Some workers are in the habit of emphasizing the ‘ liquid 
nature ’ of protoplasm, and of regarding the living substance as miscible in water, apparently, 
therefore, assuming that the living colloid is an emulsion of protoplasm in water rather than one of 
water in protoplasm. Such excessive imbibition as above described could have been manifested only 
by a colloidal jelly. It is further of interest to note that this highly swollen protoplasmic jelly 
continues active streaming. 
2 A more detailed description of the effect of the saponins and of other toxic substances on 
protoplasmic streaming is given in an article recently published (20), to which the reader is referred. 
