Permeability 49 
has a structure, but it must be emphasized that this structure is 
ultra-microscopic and not coarse enough to be observed under the 
ordinary microscope as was at one time thought. The production 
of a reticulate structure in the cytoplasm when treated with 
fixing and staining agents led to the view that cytoplasm possessed 
a net structure visible under the microscope. Even if the views of 
some earlier writers more or less dimly suggest the opinion that 
cytoplasm is in the colloidal condition, and while Biitschli (1892) 
suggested that living protoplasm has the structure of a microscopic 
emulsion, it was Hardy (1899) and A. Fischer (1899) who showed 
that the structure of cytoplasm after treatment with fixing agents 
could be made to vary according to the treatment during fixation. 
The conclusion to be drawn is obviously that the reticulum 
generally observed is the result of the fixing, and for the reasons 
already given it must be held as undoubtedly true that cytoplasm 
is essentially a colloidal system. 
Although in many cases the body of the cytoplasm is a sol, 
there is a certain amount of evidence that in many cells the cyto¬ 
plasm may be in the more solid gel condition. Thus Bayliss (1919) 
says: “That there are possibilities of the formation of membranes, 
doubtless of a gel nature, within the protoplasm of a cell is shown 
by the fact that different reactions can take place at the same time 
in different parts of the cell, notwithstanding the general liquid 
nature of its contents/’ Gaidukov (1910) and Price (1914) by ultra- 
microscopic observation find that in some cases Brownian move¬ 
ment in the cell may cease, and suppose the protoplasm in these 
cases has taken on the state of a gel. 
Price concludes that protoplasm can, and often does, exist in 
the gel state, and in this state may be active. Bayliss has been 
able to bring about the cessation of Brownian movement by weak 
electrical stimulation and relates the phenomenon with functional 
activity (1919). Chambers (1917), by microscopic observations made 
on dissections of living cells, also comes to the conclusion that in 
the ova of a number of marine organisms (Asterias, Arbacia, Echino- 
arachnius, Cerebratulus, Fucus) and in the germ cells of certain 
insects (. Periplaneta , Disosteira, Anasa) as well as in protozoa, the 
cytoplasm usually exists as a sol. On the other hand he considers 
that in adult somatic cells, including nerve cells and muscle fibres, 
the protoplasm forms a more or less rigid gel. Leucocytes however 
possess a cytoplasm closely resembling that of germ cells. Seifriz 
(1918,1920) also, in a similar series of observations on Myxomycetes, 
