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Walter Stiles 
(1909) to be soluble in lipoid substances, but yet did not stain most 
cells. Hober showed that wool violet may be actually absorbed but 
undergoes a change in the cell resulting in decolorisation, as this 
can be effected by treatment of the dye with fresh frog’s liver. Kuster 
(1911) found all these dyes were absorbed by some, although not all 
plant cells. However, Collander has shown that cells of sugar beet 
and Elodea do not absorb wool violet 5 with any rapidity. There 
appears to be some doubt whether this dye should be regarded as 
a typical lipoid-soluble dye, as an experiment made by Collander of 
the partition of the dye between water and a saturated solution of 
cholesterol in benzene resulted in the dye going in greater quantity 
to the water. 
Hober also points out that in another group of acid dyes, the 
phthaleins, there are a number which are soluble in lipoid substances 
but which do not stain living cells, namely, rose bengal, cyanosin, 
erythrosin and gallein. 
Ruhland also states that new blue R is a dye insoluble in lipoid 
substances, but which stains living cells. Even methylene blue, one 
of the most easily absorbed dyes, prefers water to lipoids (Loewe, 
1912). However, Hober and Nast found new blue R was soluble in 
a solution of cholesterol in turpentine. The absorption of many 
sulphonic acid dyes by certain plant cells as shown by Kiister’s 
method, appears to tell against the lipoid theory, as these dyes are 
in general insoluble in lipoid substances. 
It is clear that a simple lipoid theory will not explain the behaviour 
of all cells to all dyes, but the principal difficulty arises from the 
intake of inorganic salts which are as a rule insoluble in lipoid sub¬ 
stances. Consequently the theory has to admit that substances 
insoluble in lipoids may, under certain circumstances, be able to 
penetrate into the cells. Hence we find solution theories put 
forward in which the plasma-membrane is regarded as a mosaic 
(Nathansohn, 1904#) or a colloidal complex (Lepeschkin, 1910 a, b, 
1911 a, b, c) (cf. Chapter vm) in which lipoid substances are present, 
by solution in which dyes, narcotics and other lipoid-soluble sub¬ 
stances enter the cell, and in which there is also an aqueous phase 
through which water-soluble substances such as inorganic salts, acids 
and bases, and sugars, are able to diffuse into the cell. 
The lipoid theory is at best an imperfect theory, only professing 
to indicate, as Collander puts it, what substances will enter all cells 
easily under all conditions. But even thus restricted the theory 
appears to break down, for, as already indicated, there are substances 
