122 American Fisheries Society 



osmosis. This principle of osmosis is of almost universal 

 application in nature, and is used by men in the arts, but a 

 good understanding of it is not common. By osmosis our 

 food is taken from the intestines to the blood without any 

 communicating opening ; by osmosis, oxygen is taken from the 

 air into the blood, without any leakage of blood; by the same 

 principle the kidney tubules remove undesirable substances 

 from the body while holding back all desirable substances; 

 by osmosis the roots of plants select the necessary minerals 

 from the soil; a weak sugar solution will readily ferment, 

 but if made concentrated it destroys yeast and bacteria by 

 osmosis, and is therefore an excellent preservative of fruits. 

 Salt is also a preservative by virtue of its concentration. Any 

 other neutral mineral substance equally soluble would preserve 

 in the same way that salt does, but salt happens to be the only 

 one that the human palate and stomach will tolerate. 



HOW SALT EXTRACTS WATER 



At the risk of appearing verbose, the writer undertakes to 

 elucidate the principles that govern osmosis because osmosis 

 is nearly the whole principle of salting fish. Without a 

 knowledge of osmosis people may salt fish successfully by rule, 

 but without such a knowledge it is quite impossible to under- 

 stand the process. 



If a thin animal skin or membrane separates two liquids, 

 and if the liquids are alike, nothing happens. But if they are 

 unlike, one or the other, or both, of the liquids will pass 

 through the skin to the other side; this passage through the 

 skin or membrance is called osmosis. Just what components 

 pass through the membrane, and in what direction, and how 

 much, depends on many circumstances. For the purposes of 

 salting fish, water is always the liquid, plus whatever is dis- 

 solved in the water, and the skin and cell-membranes are the 

 dividing membrane. We thus have water and salt outside, 

 cell-membrane between, and fish juice or protoplasm inside. 



