KATABOLISM. 



431 



1. We have alluded (page 419) to the importance of 

 the quick removal of the products of katabolism. Stop 

 respiration, and death by blood poisoning takes place in 

 five to ten minutes. If the function of the kidneys stops, 

 death by blood poisoning (uraemia) occurs in twenty-four 

 to forty-eight hours. See, then, the much greater im- 

 portance of the lungs. 



2. It is on account of this supreme importance that 

 in the higher animals the whole of the blood passes 

 through the lungs, that there is complete double cir- 

 culation, and that blood completely purified of CO g goes 

 to the tissues. On the contrary, only a portion of the 

 blood passes through the kidneys ; the renal circula- 

 tion is only a branch of the systemic circulation, and 

 therefore only mixed blood, so far as urea purification 

 is concerned, goes to the tissues. But it will be remem- 

 bered that the same is true of the pulmonic circulation 

 in reptiles and amphibians. 



3. Of foods, amyloids and fats are wholly removed 

 by the lungs, while the albuminoids are divided between 

 the lungs and the kidneys in the manner already ex- 

 plained. Of the elements of organic matter, the larger 

 part of the C, H, and O is removed by the lungs, but 

 the whole of the N, S, and P by the kidneys. 



4. The lungs not only eliminate C0 3 and H 2 0, but 

 take in O for combustion. The function of the kidneys, 

 on the contrary, is purely eliminative. The eliminated 

 product in case of the lungs is the result of oxidation ; 

 in the case of the kidneys, of decomposition. 



5. The circulation of the elements of organic matter 

 back to the atmosphere is through both of these organs. 

 The return of C in the form of C0 2 is through the lungs ; 

 the return of N in the form of ammonia is through the 

 kidneys as urea, which, as we have seen, is quickly 

 changed into carbonate of ammonia. Thus all the ele- 



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