INFLUENCE OF THE MEDIUM 125 



erties coexist in the same solution, it is possible and prob- 

 able that the organism may often be affected in both ways 

 at the same time. 



By the chemical properties of a solution are meant the 

 chemical nature of the solute or solutes. It is to be expected 

 that a solution of cuprous sulfate will affect organic beings 

 differently from a solution of cane sugar or one of sulfuric 

 acid; these solutions are chemically very different. By 

 physical properties are meant such qualities as viscosity, 

 transparency, surface tension, osmotic pressure, etc. The 

 latter is the only one of these which it is necessary to con- 

 sider here. This property of osmotic pressure has been 

 shown to be of general importance to the living being 

 grown in ordinary nutrient solutions, but it has long been 

 neglected in experiments with such solutions. Experi- 

 menters with nutrient fluids have varied the chemical nature 

 of their solutions without taking into account the fact that in 

 so doing they were very probably varying the osmotic pres- 

 sure also. 



When these workers have dealt with very weak solutions 

 only, it is evident that the error thus introduced is practi- 

 cally negligible ; the osmotic pressure must be very slight 

 in all cases. Thus Ono l showed that various mineral salts 

 which are usually considered as poisons have an acceler- 

 ating effect upon the growth of certain fungi when the 

 solutions are very dilute. In this case the osmotic pressure 

 is of such a low order that it may be left out of account. 

 But suppose a case of another sort. It is also well known 

 that a stronger solution of such a salt as cuprous sulfate will 

 produce almost instant death. Shall it be argued, then, 

 that life or death depends upon the number of Cu and SO 4 

 ions which may penetrate the living cells ? Or shall it be 



i N. ONO, " Ueber die Wachsthumsbeschleunigungeiniger Algen und Pilze durch 

 chemische Reize," Jour. Coll. Sci. Imp. Univ. Tokyo, Vol. XIII (1900), Part I: Bat. 

 Mag., Vol. XV (1900), p. 75; reviewed in Bot. Gaz., Vol XXX (1900), p. 422. 



