196 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



and it seems to me that despite the discoveries of ISTathan- 

 sohn that certain algae and cells of higher plants are 

 able to change the permeability of their surfaces in a 

 way which regulates the distribution of single salts or 

 ions in the sap of their cells without any regard to pure 

 osmotic equilibrium, such a simple explanation might be 

 possible. 1 



There are many regulation phenomena connected with 

 osmotic pressure and permeability in animal physiology 

 also, though at present they are not worked out as fully as 

 possible. The works of Fredericq, J. Loeb, Overton and 

 Sumner 2 would have to be taken into account by any one 



von Mayenburg's experiments the organism itself is actively at work. As to 

 compounds liable to ionisation, it has been noticed by Maillard that a certain 

 regulatory character is contained simply in the physical fact that the degree 

 of ionisation changes with concentration : decrease of concentration for instance 

 would be followed by an increase of ionisation, and so the osmotic pressure 

 may be preserved (C. rend. Soc. Eiol. 53, 1901, p. 880). 



1 In the different experiments of Nathansohn (Jahrb. wiss. Bot. 38, 1902, 

 and 39, 1903) the salinity of the medium was changed in such a way that 

 there was in each case either an abnormal increase or an abnormal decrease in 

 the concentration of one single ion necessary for metabolism. The cell was 

 found to stand these abnormal changes in such a way that in the case of the 

 increase of the concentration of the medium it did not allow more than 

 a certain amount of the ion in question to come in, and that in the case of 

 the decrease it did not allow more than a certain quantity of the ion to go 

 out. It thus seems as if the permeability of the surface were adjusted 

 to a certain minimum and to a certain maximum of every single ion or 

 salt, the permeability being stopped from within to without, whenever the 

 minimum, and from without to within, whenever the maximum is reached 

 in the cell sap ; both irrespective of proper physical osmotic equilibrium 

 (" Physiologisches Gleichgewicht "). Thus, in fact, there only would be a 

 case of primary regulation, nothing more. It would all appear rather similar 

 to what occurs in the kidney. Of course we do not assert that our explana- 

 tion is right, but it is possible and is at the same time the most simple, and 

 it is our general practice always to prefer the most simple hypotheses. 



2 Many fishes are able to withstand great changes in the osmotic pressure 

 of sea-water ; the osmotic pressure of their body fluids, though never in a 

 real physical equilibrium with the pressure of the medium, nevertheless may 

 vary whenever the abnormal conditions of the latter exceed certain limits. 



