126 REPORTS ON THE STATE OF SCIENCE.—1918. 
obtained from the mode of production of the membrane. If it is 
composed of materials contained in the protoplasm of the cell it will 
naturally vary its nature according to the state of the cell, while, 
being a complex colloidal mixture, it will be easily accessible to the 
influence of electrolytes. But what actual evidence have we that it 
may become permeable to electrolytes under any conditions ? 
Direct proof of such changes under natural conditions is clearly 
difficult, but Lillie (1913) noticed that the cells of the larva of 
Arenicola when in a state of contraction lost their normal pigment, 
which is usually in solution in the cell contents. Garmus (1912) 
found that certain secreting cells beca less permeable to dyes 
under the influence of atropine, more permeable under pilocarpine. 
The point of these observations is that pilocarpine excites glands to 
activity ; atropine stops their activity. Indirect proofs are more in 
number. The change of electrical conductivity already referred to is 
a convenient means of detecting changes_of permeability. The egg 
cell on fertilization increases in conductivity (McClendon, 1910, 
Gray, 1916), as also does the muscle cell on contraction (McClendon, 
1912). The movements of the sensitive plant are usually ascribed to 
an increase of permeability of the cell membranes of the lower side 
of the “pulvinus.” In this way the cells, which are normally 
distended owing to the osmotic pressure of certain solutes in their 
interior, lose these solutes and thus the distension due to their 
osmotic pressure. Blackman and Paine (1918), however, show that, 
although there is evidence of a very small escape of electrolytes, it is 
too small to account for the phenomenon, which can be repeated 
many times with the tissue immersed in warm water. They consider 
it more probable that the loss of turgor is due to a sudden decrease in 
concentration of osmotically active substances in the cell. 
The effects of certain agents on the cell, producing a temporary, 
reversible increase in permeability of the membrane, show how the 
necessary changes might be produced. The. most instructive are 
those produced by inorganic salts. Ringer (1882) was the first to 
show that the frog’s heart is incapable of continued activity in a pure 
solution of sodium chloride, even of the correct osmotic concentration, 
whereas the addition of salts of calcium and of potassium in relatively 
small amount enabled the beats to continue indefinitely. A large 
number of experiments on such “ balanced solutions” were made by 
Loeb (1901 and onwards) and brought into relation with changes ° 
in the permeability of the cell membrane. The experiments of 
Osterhout (1911) on the seaweed, Laminaria, showed that the tissue 
increased greatly in electrical conductivity when immersed in asolution 
equivalent to sea water, but containing sodium chloride only, returning 
to its normal state on the addition of a certain proportion of calcium 
chloride. No permanent damage was done to the cells (Osterhout, 
1915) by repeating the experiment many times. The explanation 
given by the investigator himself is not quite clear, but to the present 
writer it seems to be as follows: As we saw above, the cells in 
normal conditions are non-conductors -because their surface mem- 
branes do not permit the passage of ions. Under the influence of © 
sodium ions these membranes become permeable and allow free 
movement of ions carrying electric charges through them, Calcium 
