148 PHYSIOLOGY OF NUTRITION. 



the methyl-blue-containing solution of Bisodium phosphate, we 

 shall find that the colouring 1 matter now soon passes through the 

 parchment into the water. In my experiments the water was 

 clearly tinged at the end of two hours. Precipitation membranes 

 of Calcium phosphate are permeable to Sodium chloride, as we 

 may of course readily ascertain. These experiments, it is to be 

 specially emphasised, are only intended to prove that particular 

 substances which can traverse one membrane are often unable to 

 pass by osmosis through another. Such experiments are obviously 

 of particular interest in examining the behaviour of certain sub- 

 stances towards the cell-wall on the one hand, and the proto- 

 plasm on the other. But whether a substance which cannot 

 traverse an artificial membrane is at the same time unable to 

 penetrate into the protoplasm, can only be determined by special 

 observations in each case ; and as regards methyl blue, it is to be 

 observed that as a matter of fact it can pass through the proto- 

 plasm into the interior of the cells. 



If plants of Elodea canadensis are left for twenty-four hours in 

 a 0'0008 per cent, aqueous solution of methyl blue (we use a litre 

 of the fluid), microscopical examination of the leaves shows that 

 their cell- sap is coloured deeply blue. The cells are not dead, for 

 they exhibit protoplasmic movement, and we see therefore that the 

 colouring matter must have traversed the cell-wall and also the 

 protoplasm. 2 



To judge from the results of our investigations, many substances 

 (colouring matters, sugars, vegetable acids, mineral substances) 

 are frequently not able as such to pass by osmosis through the 

 ectoplasm of the protoplasm. But it does not follow that the 

 hyaloplasm is under all conditions impermeable to these sub- 

 stances. Recent investigations of different observers which, 

 however, are still by no means completed lead rather to another 

 view. It appears that certain substances which cannot usually 

 traverse the protoplasm, can make their way through it when 

 active accumulation is taking place in the cells. Probably also the 

 hyaloplasm varies in its osmotic properties in consequence of the 

 vital processes themselves, and in accordance with the require- 

 ments of the cells, but continued energetic investigation will be 

 required to throw light on these matters. 



1 Literature : Sachs, Fxperimentalphysiologie d. Pflanzen, 1865, p. 447, where 

 particularly the important work of Nageli is discussed. Also de Vries, Archives 

 Neerlandaises, 1871, T. 6, and Pringsheim's Jahrbucher, Bd. 16, p. 588; 



