Chapter 2 



WATER 



Occurrence and importance 



Water is the most abundant substance in living matter. The great 

 physiologist, Claude Bernard, said, "All living matter lives in water." 

 In his Outline of History, Wells put it this way, "We talk of breathing 

 air, but what all living beings really do is to breathe oxygen dissolved 

 in water." 



Table 2-1 gives the water content of some typical animal, plant, and 

 microbial materials. The human body is about 65 per cent water, a corn 

 plant about 75 per cent, and a bacterial cell about 80 per cent. The 

 amount of water varies not only with the type of material but also with 

 its period of development. Two examples, for which we have adequate 

 data, will show the variation with age. The pig embryo at 15 days of 

 development consists of 97 per cent water and 3 per cent solids, and 

 at birth the young pig is made up of about 89 per cent water and 11 

 per cent solids. The water content continues to decrease as the pig 

 grows, being about 67 per cent at 100 lbs. weight and 43 per cent for 

 a very fat animal weighing 300 lbs. The same relationship between 

 water content and age holds for other farm animals and also for man. 



The water content of the corn plant remains practically constant, about 

 88 per cent, during the actively growing period from the seedling to the 

 tassel state, decreases rapidly to around 70 per cent at the time the 

 kernels begin to glaze, and falls to about 52 per cent when the plant is 

 mature and ready to harvest. 



A high water content is characteristic of youth and activity and a 

 lowered figure is associated with old age and inactivity. The relation 

 between water content and activity of tissues is further demonstrated by 

 comparison of different tissues in the same individual. The metabolically 

 active tissues of the body, e.g., brain and liver, contain much more water 

 than the relatively inactive portions such as bones and fatty tissues. 



