Permeability 213 
A number of salts were found to act in the same way, namely, the 
chlorides of potassium, caesium, rubidium, lithium, ammonium and 
magnesium 1 ; sodium bromide, iodide, nitrate, sulphate and acetate. 
On the other hand the salts of bivalent metals examined (magnesium, 
calcium, barium, strontium, manganese, cobalt, iron, nickel, zinc, 
cadmium and tin) produce first a rise in resistance, then a fall 
(Osterhout, 1915 d); the same is the case with salts of trivalent and 
tetravalent metals (Osterhout, 1915 e). The same effect is produced 
by ether, chloroform, chloral hydrate and alcohol (Osterhout, 1913 a, 
1916/), by potassium cyanide (Osterhout, 1917 a) and by sodium 
taurocholate (Osterhout, 1919 b). 
On the assumption that electrical conductivity is a measure of 
permeability these results are interpreted as indicating that the 
substances of the first group bring about an increase in the perme¬ 
ability of the cell, while those of the latter bring about first a decrease 
in permeability followed by an increase. For the same reasons small 
quantities of sodium hydroxide are held to increase permeability 
(Osterhout, 1914 g) while hydrochloric acid is considered to produce 
rapid decrease of permeability followed at once by rapid increase 
(Osterhout, 1914 h). 
If the tissue is only allowed to remain in the single salt solutions 
for a short time and is then returned to sea water, the original 
resistance of the tissue is regained. This is regarded by Osterhout 
(1912 b, 1915 b) as indicating reversible changes in permeability. 
Reasons why electrical conductivity cannot be regarded as an 
accurate measure of permeability have already been advanced in 
Chapter xi and need not be repeated here. Also it seems to the 
present writer meaningless to speak of the permeability of the cell 
as a quantity with a definite value which can be accurately measured, 
unless the substance, the penetration of which is in question, is also 
stated, for there is no evidence that if the permeability of the cell 
to one substance changes, its permeability to all other substances 
changes in the same proportion. Osterhout’s theory of antagonism 
described in the last chapter has been extended to include reversible 
changes of electrical conductivity (Osterhout, 1920 a , b), but as 
it is highly speculative, it will not be dealt with further in this 
place. 
Trondle (1920) investigated the effect of acids on the permeability 
to sodium chloride of the cells of the leaf of Buxus sempervirens by 
a plasmolytic method in which were recorded the concentrations of 
1 But magnesium salts appear in Osterhout’s second group. 
