224 THE PRINCIPLES OF AGRICULTURE 



these organs without causing irritation or de- 

 rangement. 



408. Another important liver function is the 

 transformation of peptones (which are poisonous 

 when thrown into the blood in any considerable 

 quantity) into products which are non-poisonous, 

 and are capable of assimilation. These pro- 

 ducts form tissue, or fulfill some other im- 

 portant use in the body. 



409. Still another important use of the liver 

 is to transform into harmless compounds the 

 poisonous products of bacterial fermentations 

 (such as ptomaines and toxins). These occur 

 in the contents of the intestine, and might often 

 prove deadly if allowed to pass this guardian 

 sentinel — the liver — in any considerable amount. 



5. Respiration J or Breathing 



5a. What breathing is 



410. Breathing consists in the substitution of 

 oxygen of the air for carbon dioxid in the blood 

 and tissues of the animal body. It results in 

 the combination of the oxygen, of the air with 

 certain organic constituents of the system ; and 

 it fits these constituents for various uses, or for 

 eUmination as waste matters. 



