THE INTEGRATIVE ACTION OF THE VASCULAR SYSTEM 229 



would be easily detected alterations after the drinking of 

 large volumes of w^ater such as described. 



When need arises water is withdrawn from the stores. 

 After bleeding there is a sudden demand. The largest amount 

 of the released fluid comes from the muscles (though they 

 lose only }i of i per cent of their weight) and the next 

 largest amount comes from the skin. Other parts give up 

 their reserve as well. Among the other organs are the sahvary 

 glands. The saliva which they produce is more than 98 per 

 cent water. When the water supply fails, therefore, they 

 cannot provide an adequate amount of saliva to keep the 

 throat moist. In consequence disagreeable sensations of 

 dryness and stickiness arise from that region, sensations 

 which we call thirst. This leads to the drinking of water 

 and thus to restoration of the normal supplies in the body 

 and to resumption of the normal service of the salivary 

 glands. 



The Constancy of Temperature. One of the most striking 

 and easily observed constants of the internal environment 

 is that of the temperature in the "warm-blooded" animals. 

 Although there is a daily swing from a low point about 

 4 A.M. to a high point about 4 p.m., the variation is hardly 

 more than a degree in the Fahrenheit scale. The constancy 

 is so reliable that the thermometer makers can stamp 

 98.6° on the scale with assurance that it will mark closely 

 the temperature of the normal person everywhere. The 

 value of uniform temperature is demonstrated by comparing 

 the influence of cold on ourselves and on lower animals 

 without a regulatory mechanism. As the weather becomes 

 cold the frog, for example, becomes more and more sluggish, 

 until finally he sinks inactive to the bottom of his pool and 

 thus remains unless he is warmed again. This behavior is 

 determined by the direct dependence of the speed of chemical 

 processes in the body on the degree of heat. The "cold- 

 blooded" animals, having the temperature of their surround- 

 ings, can act with speed only when the weather is warm; 

 the warm-blooded, maintaining a fairly fixed high tempera- 

 ture in spite of external cold, can act with speed at all times. 

 There is no better illustration than this of the value of the 

 even tenor of our internal environment as a condition for 



