METABOLISM AND FOOD 99 



(i) The effect of water. 



Water plays a very important part in the animal 

 economy. Its first duty is to facilitate the chewing 

 and swallowing of the food. In the processes of 

 digestion and in the absorption of the soluble sub- 

 stances in the body water is again necessary, for 

 solutions which are too concentrated do not pene- 

 trate the walls of the alimentary canal, but rather 

 draw water from them. This causes increased 

 movement of the intestine (peristalsis) and its 

 premature evacuation. Water serves further as 

 a transporter of the nutrients in the blood and 

 lymph vessels and for the excretion of the final 

 products of metabolism. It is connected also 

 with the loss of heat from the body, for by its 

 evaporation, either from the skin or lungs, there is 

 a considerable lowering of the temperature. In 

 this way an excess of heat, which is always the 

 result of high feeding or hard, muscular work, is 

 prevented, for this might otherwise lead to a fatal 

 overheating of the body if a sufficient quantity of 

 water were not there. 



A lack of water, it will then be understood, 

 would cause all sorts of disturbances both in the 

 metabolism of the food and in the general condition 

 of the animal. Observations on men and on 

 different animals have shown that when too little 

 water is taken the gastric digestion and the passage 



