WATER. 79 



nor dissolve and hold in solution the nutritive materials which 

 it supplies to the tissues, nor carry the waste materials to the vari- 

 ous organs whose duty it is to eliminate them. Without water the 

 saliva would cease to be the important agent it is in softening the 

 food in the mouth preparatory to its being swallowed. In short, 

 without water as an integral part of the fluids of the body these 

 fluids w r ould cease to be fluids, and the many and varied offices 

 which they subserve would at once be abolished, and life could no 

 longer be maintained. 



Equally important, though less apparent, are the various offices 

 which are subserved by water in the solids of the body. From 

 the above table it is seen that water exists in the muscles to the 

 amount of 73 per cent. The striking property of muscles is their 

 power of contractility, or ability to shorten. By the exercise of 

 this property all the movements of the different parts of the body 

 are accomplished : without this power locomotion would be impos- 

 sible, the movements of the heart would cease, and death would 

 quickly supervene. A muscle deprived of its water would cease 

 to possess this contractile power in other words, would lose its 

 characteristic function. It must not be inferred from this, how- 

 ever, that it is to the water that muscles owe their contractility, 

 but simply that its presence is one of the conditions essential to 

 the exercise of this power. As will be seen later, the skin pos- 

 sesses most important functions those, for instance, of sensation, 

 of excretion, and of protection. All these functions would be 

 destroyed if the water in the skin was expelled. Perhaps this 

 fact is nowhere more strikingly evident than in studying the func- 

 tions of the skin of the palm of the hand. The pliability of this 

 portion of the skin, by which objects are grasped, and the sense 

 of touch, by which it can be determined whether they are hard 

 or soft, whether rough or smooth, whether hot or cold, are both 

 dependent on the presence of water in the skin, and the mere 

 evaporation of the water would at once make the skin hard and 

 rigid, its pliability would vanishj and its functions would cease. 



Sources of Water. The water which exists in the body is derived 

 from two principal sources : First, from the food, and second, from 

 its formation in the interior of the body, the former being the 

 main source of supply. As water is a constituent part of every 

 tissue of the human body, so it is of all the varieties of food, both 

 solid and liquid, taken into the body. 



The quantity of water in food (percentage) is as follows : 



Wheat bread (fresh) 33 



Mackerel 70 



Lean beef 70 



Potato 76 



Human milk 87 



Cows' milk 87 



Green vegetables 88 



