THE EXCRETORY SYSTEM 227 



The actual cause is not known, but the symptoms are 

 striking. The disease is characterized by a noticeable yellow 

 hue of the skin and very dark urine. The colors are some- 

 times so deep as to be alarming, but the trouble is not serious 

 as a rule, and soon disappears. The real cause of none of these 

 several diseases is as yet known. They do not seem to be 

 produced by disease germs, and none of them are contagious. 

 No methods of avoiding them are known beyond the general 

 one of maintaining good health by proper exercise and diet, 

 avoiding overeating and stimulants. 



