273 
Protoplasm by Aid of Microdissection . 
vacuoles, and ‘ the bodies of every kind contained in the protoplasm The 
ultra-modern tendency is — and I quote from Berczeller’s ( 5 , p. 61) work on 
the physical chemistry of membranes — c not to speak of “ walls”, “skins”, 
or “ membranes We must not picture to ourselves a rigid layer, as the 
osmotic theory really demands but which has in animal cells never been 
observed ; but we are dealing rather with liquid surface layers which in 
many cases . . . can also assume a solid form.’ This reaction to the old 
notion of a plasma-membrane culminates in the school led by Fischer ( 15 , 
p. 158), who believes that ‘There are no membranes about cells’. Indeed, 
so fearful have some become of giving credence to the existence of a true 
protoplasmic membrane that they are now quite satisfied with a layer of 
but two molecules in thickness to which to ascribe all permeability 
phenomena. 1 
Before discussing the experimental data which have led me to agree 
essentially with Berczeller in looking upon the plasma-membrane not as 
a skin, but as a highly viscous layer of modified protoplasm which may at 
times become quite fluid, it will be well to consider some membranes and 
surface layers which are pretty well recognized, chiefly with the view of 
excluding them from the discussion. 2 
Certain unicellular organisms are known to possess definite and readily 
isolated membranes ; e. g. Vorticella has a tough membrane and Euplotcs 
possesses a quite resistant pellicle. There is no contention over the 
existence of these structures. They may be said to be true membranes in 
the unqualified biological sense. There are, however, other unicellular 
organisms, such as Paramoecium burs aria and many species of Amoeba , which 
are generally considered ‘naked’. (Some Amoebae are said to possess 
a membrane of appreciable thickness. Vonwiller, 44 , p. 286.) In marine 
ova there may or may not be an easily recognizable membrane. In Fucus , 
e. g., there is an egg-wall measuring 1 /x in thickness. In Asterias and 
Cerebratulus the eggs are surrounded by a membrane which, on fertilization 
(Asterias) or escape into sea- water (Cerebratulus), lifts off to form the ferti- 
lization membrane. In the Arbacia egg there is said to be no discernible 
membrane, therefore the fertilization membrane must be a precipitation 
product or a new secretion ( 19 , p. 239). These generally recognized and 
readily discernible membranes — 5 non-cellular secretions ’, which, in the 
zoological sense, are probably synonymous with the cell-wall of plants — are 
not the subject of the following discussion. We are concerned only with 
so-called ‘ naked’ protoplasm, of which myxomycetes, most Amoebae , and 
all escaped protoplasm are examples. The same type of membrane which 
1 Personally, I cannot believe that a two-molecule layer, i. e. a surface tension membrane, is 
sufficient for any differential permeability phenomena. 
2 I prefer to keep the expression 1 plasma-membrane ’ for the superficial layer of protoplasm. 
Little clarity will be gained by the substitution of any other name, old or new, until we have more 
real knowledge of the actual structure and composition of the plasma-membrane. 
T 
