166 PHYSIOLOGY FOR BEGINNERS CHAP, xiv 



surface and less to the internal organs. More urine excreted 

 means only more water discharged from the blood by the 

 kidneys, for the amount of urea and other substances dis- 

 charged in a day does not vary much as the result of changes 

 of temperature ; it is the amount of water discharged with these 

 substances which chiefly varies. When in cold weather less 

 water leaves the body by the skin as perspiration, more leaves 

 by the kidneys, so that the skin and the kidneys work, in this 

 respect, hand in hand. The presence of much water in the 

 blood, such as is brought about by drinking a large quantity 

 of fluid, leads also to an increase in the flow of urine. 



