THE HESPIRATOKY SYSTEM 121 



the first is largely derived from oxidation of the various organic 

 compounds of the body and is the guide to the extent of tissue 

 activity, while the second comes, in most part, from the destruc- 

 tion of cellulose in the intestines. 



co 2 



O and CH 4 N 



100 cc. arterial blood 20 cc. 38 cc. 1 . 5 cc. 



100 cc. venous blood 10 cc. 48 cc. 1 . 5 cc. 



Difference 10 cc. 10 cc. . cc. 



This table represents the difference between the gases in arte- 

 rial blood and those in venous blood. It shows that there is 

 always a considerable amount of deleterious gases in arterial 

 blood, and a corresponding amount of life-giving oxygen 

 in venous blood. Furthermore, it shows that the tissues do not 

 remove all the oxygen, nor do the lungs remove all the carbon 

 dioxid and methane from the blood circulating through them. 



The other theory is based on the fact that the lung and capil- 

 lary endothelial cells, which form very thin walls through which 

 the gases must pass, have the power actually to absorb and to 

 secrete gases. This property has been termed "vital action" 

 in lieu of more specific knowledge. In these premises it is not 

 necessary to have physical forces operating. Many investiga- 

 tors have attempted to duplicate the experiments but have 

 not entirely succeeded. The theory is therefore not generally 

 accepted. 



Throughout the entire existence of the animal the waste prod- 

 ucts which are formed in the tissues as a result of oxidation are 

 removed by the process of internal respiration. The source of 

 these products and the method by which the body disposes of 

 them will now be considered. 



The oxidation of proteins (amino-acids) in the tissues results 

 in the formation of ammonia and other waste products which are 

 taken to the liver and converted into urea. This substance is 

 passed to the kidneys for excretion. Some water and carbon 

 dioxid are also produced; the former escapes through the lungs, 

 the kidneys, and the skin, while the latter is largely disposed of 

 by the lungs in the exhaled air. 



The oxidation of fats in the tissues takes place according to the 

 following equation : 



C 5 iH 98 06 + O = 51C0 2 + 49H 2 

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