WATER ^ 



Table 2-1 

 Water conlenl of some important biological miiterials 



Water 

 Material [per cent] 



Human body 65 



Brain, gray matter 84 



Liver 76 



Muscle 73 



Blood 80 



Milk 87 



Saliva : . . 99.5 



Bone 10-40 



Adipose tissue (mainly fat) 10-30 



Larvae of clothes moth 58 



Pig embiyo, 15 days old 97 



Pig at birth 89 



Pig at maturity, depending on fatness 40-50 



Cora i)lant, seedling to tassel period 85-90 



Com plant, kernels glazed 68-72 



Corn plant, maturity 50-60 



Bacteria 73-90 



Yeasts 68-83 



Molds 75-85 



It is all too common a fallacy to limit the meaning of "foods" to the 

 energy-yielding materials — carbohydrates, fats, and proteins — with the 

 inclusion perhaps of mineral elements. If the term food be considered 

 to include all substances that are essential for the growth and repair 

 of body tissue, as most certainly it should, then water likewise is truly 

 a food. This error in thinking has arisen from the fact that in the 

 past most biologists have treated water as if it were an inert material 

 and have looked upon the solids of plant and animal tissues as the im- 

 portant part of the organism. Gortner has pointed out how mistaken 

 is this view; he illustrates his argument by citing the composition of 

 the tadpole, 95 per cent water and 5 per cent solids. "It would be 

 ridiculous to speak of this organism as being composed of only 5 per 

 cent of vital materials. The water is as much a part of the tadpole as 

 arc the fats, proteins, etc., which serve to form the gel structure, and the 

 biochemical and biophysical reactions which take place within the cells 

 and tissues of the tadpole are determined probably more by the water 

 which is present than by any or all of the other constituents." 



Free and bound water 



The term "bound water" has come into use to designate water that has 

 been adsorbed by the colloids of the living cell, in contrast to "free water," 



