287 
Protoplasm by Aid of Microdissection . 
‘ This border value (i.e. the thickness of the membrane upon which certain 
surface-tension values depend) is just twice the effective radius of molecular 
forces . . These suggestive values are mere analogies, but there is good 
reason to suppose, because of the similarity in physical properties and 
method of formation, and of actual, albeit rather crude, estimation, that the 
thickness of the plasma-membrane is of the order of magnitude of precipi- 
tation membranes, namely o*cooi mm. (o-i /x). 
It is of value as well as of interest to consider the findings of physicists 
who step temporarily into the field of biology to work upon living material 
in order to compare the phenomena observed there with similar phenomena 
seen in the inorganic world. Quincke ( 34 , p. 62 9), in working ^upon the 
cells of Char a, Elodea , &c., found that the two masses of protoplasm which 
have become separated as a result of plasmolysis of a cell do not always 
unite on coming together when the protoplasm swells, but are separated by 
a film similar to that which surrounds the entire protoplast. Comparing 
the physical properties of this film with those of solid and liquid lamellae of 
inorganic precipitates, Quincke concludes that this protoplasmic film is 
‘ a very thin liquid membrane \ Lehmann ( 24 , p. 409) also believes that the 
comparison of the liquid membranes of artificial cells with the living plasma- 
membrane is of more than merely superficial significance. 
Attempts on my part to establish the presence of a plasma-membrane 
through observation with the ultra-microscope were unsuccessful. Though 
it was possible to observe the vibration of colloidal particles in the hyaline 
matrix of myxomycetes, there was no distinct outer layer discernible by aid 
of dark ground illumination. 1 
Summary. 
1. The direct evidence from microdissection indicates the existence of 
a plasma-membrane on the surface of all protoplasm. 
2. The indirect evidence derived from a consideration of surface 
phenomena strongly supports the belief in a differentiated surface layer of 
protoplasm. 
3. The plasma-membrane is essentially protoplasm, although it differs 
in physical properties, and probably also in chemical constitution, from the 
mass of plasma which it bounds. 
1 Gaidukov (16, p. 50), in connexion with his observations on botanical material by means of 
the ultra-microscope, says, ‘ The cell membrane exhibits a pronounced optical inhomogeneity, which 
does not interfere with the investigation of the cell contents ’. The last clause of this sentence makes 
one wonder if Gaidukov actually has reference to the plasma-membrane. The German word 
‘ Zellmembran ’ is synonymous with £ Zellhaut which is the ‘ Plasmahaut ’ or plasma-membrane. 
It is unfortunate that he does not describe his observations in greater detail if he was actually able 
to distinguish the protoplasmic membrane by aid of dark-ground illumination. He (16, p. 74) does, 
however, say, 1 The hydrosol complex of protoplasm (cytoplasm) is protected by a hydrogel layer 
(plasma-skin) . , 
