EXCRETION AND SEWAGE 25 1 



When the intestine does not expel its contents, symptoms 

 like liver and kidney diseases arise. So the intestine 

 excretes some waste matter. Under certain conditions 

 even the stomach may become an excretory organ, and 

 vomiting may be a life-saving act, just as it often is when 

 poisons are swallowed. 



446. Intemperance and kidney disease. Alcohol, by 

 disturbing oxidation and the liver, is especially liable to 

 cause the production of poisons whose excretion severely 

 taxes the kidneys. It alone causes over one half of kidney 

 diseases. Candies, pie, cake, and preserves are all eaten 

 simply for their taste, and usually after a sufficient amount 

 of proper food has been taken. So, in oxidizing this 

 increased amount of food, some must be imperfectly oxi- 

 dized. Thus poisons are developed and the kidneys are 

 overworked. 



Intemperance in sugar eating is extremely common. It 

 produces imperfect oxidation in the same way as alcohol, 

 only its effects are much slower and less noticeable. 



447. Sewage. The excretions of man and animals, 

 together with the dirty water used in washing, is sewage. 

 Sewage is composed of substances which are often very 

 poisonous, and often contain disease germs (p. 136). 



448. Purification of sewage. Nature is very efficient in 

 changing sewage so that it is no longer harmful. In the upper layers 

 of the soil it is fully oxidized to carbonic acid gas and water and min- 

 eral substances. The soil can dispose of a great quantity of sewage and 

 prevent it from polluting the surrounding wells. 



In the second place, plants feed upon sewage. They aid in its oxi- 

 dation and use it as food. Thus plants may form again the substances 

 which were oxidized in man's body so that he may eat the very prod- 

 ucts which he once excreted. 



In the third place, running water washes away sewage, and by means 

 of the oxygen which it always contains it fully oxidizes the excretions. 



