CHAPTER IV 



THE INFLUENCE OF THE OSMOTIC PRESSXmE OF THE 

 SURROUNDING MEDIUM UPON ORGANISMS 



I. INTEODUCTOBY 



Although many researches have been carried out to 

 determine what may be the influence upon the organism of 

 the medium in which it is grown, it is only within the last 

 few years that osmotic pressure has been investigated in 

 this regard. Most experimenters have varied the chemical 

 nature of the medium in which plants and animals were 

 grown, and have argued from their experiments that the 

 presence or absence of certain chemicals brings about cer- 

 tain effects within the organism. But if osmotic pressure 

 can have any effect upon the behavior of the living being — 

 and sufficient evidence has now been accumulated to show 

 that it does have a very marked effect — then the results of 

 all such researches must be considered as very questionable. 

 Nearly all the published accounts of the influence of nutrient 

 salts upon growth, reproduction, etc., in plants are subject to 

 this criticism, that, while the author supposed he was varying 

 a single factor, he was in reality varying at least two. Of 

 course, any conclusions reached from research of this kind 

 are not to be relied upon. 



There are always two ways in which a nutrient fluid may 

 affect the organisms placed in it, and these two ways corre- 

 spond to the two entirely different sets of properties which 

 are possessed by every solution. The solution may affect 

 the animal or plant chemically, on account of its chemical 

 properties, or it may have a physical effect, on accoimt of 

 its physical properties. Of course, since both sets of prop- 



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