EXCRETION 279 



result. Some of the diseases of the kidneys such as chronic 

 Bright's disease are among the most fatal of human mala- 

 dies. One of the most potent causes of kidney diseases 

 is a'cohol, because so much blood passes through these 

 organs that the secretory cells are especially exposed to 

 the influence of this drug. Excessive beer drinkers are 

 especially prone to kidney disease not only on account of 

 the alcohol they consume, but because of the strain im- 

 posed on the kidneys to remove the large amount of fluid 

 added to the blood. 



The liver is also an important organ of excretion not 

 only on account of the substances it discharges into the 

 intestine through the bile duct, but because it acts on 

 various products of protein metabolism, converting them 

 into urea, in which form they are given off into the blood 

 to be removed by the kidneys. Certain substances, es- 

 pecially salts, are thrown off in the perspiration of the skin. 



