CHAPTER XIII 



THE EXCRETIONS OF THE BODY 



SEVERAL organs, the skin, the intestine and liver, the lungs and the 

 kidneys, in addition to their other functions have the function of eliminating 

 various substances which are useless or harmful to the body. We place first 

 among these substances the products formed in the decomposition of the 

 foodstuffs. Substances also which enter the body in one way or another, 

 and themselves exert a harmful influence are thrown out either unchanged 

 or more or less transformed by the activity of some organ. These trans- 

 formations in many cases are for the purpose of changing harmful substances, 

 which cannot be eliminated at once, into relatively harmless ones. We have 

 already become acquainted with an example of this in the formation of urea 

 out of ammonium salts (cf. page 370). Here belong also the following 

 phenomena : 



In the putrefaction of proteid in the intestine there arise among other prod- 

 ucts indol, skatol, paracresol, phenol, phenyl-propionic acid, phenyl-acetic acid, 

 paroxy-phenyl-acetic acid, paroxy-phenyl-propionic acid, etc., all belonging to 

 the aromatic series which in part pass into the circulation. Of these the last 

 two named (the so-called aromatic oxyacids), paroxy-phenyl-propionic acid, 

 C 6 H 4 (OH) .C 2 H 4 .COOH, derived from tyrosin by the splitting off of ammonia, 

 and the oxidation product of this acid, paroxy-phenyl-acetic acid, C 6 H 4 (OH). 

 CH 2 .COOH these two pass out in the .urine mostly unchanged. The others 

 are not burned in the body, but before they come out in the urine, they undergo 

 a synthetic transformation by which they are rendered innocuous. 



The earliest known example of such transformations is the demonstration 

 by Wohler (1824) that benzoic acid, when ingested into the animal body, passes 

 over into an acid rich in carbon, but poor in nitrogen, namely hippuric acid, and 

 is excreted as such through the kidneys. Hippuric acid, C 8 H B .CO 



HKCH 2 .COOH, 



is a compound of glycocoll (ammo-acetic acid, NH 2 .CH,.COOH) with benzoic 

 acid, which is an oxidation product of phenyl-propionic acid (C G H 5 .CH 2 .CH 2 . 

 COOH) formed in intestinal putrefaction. 



The synthesis of hippuric acid takes place in the dog exclusively in the kid- 

 neys (Schmiedeberg and Bunge), but in the rabbit in other organs also such as 

 the liver and muscles. If salicylic acid, oxybenzoic acid, paroxy-benzoic acid, 

 etc., instead of benzoic acid, be fed to mammals they all undergo transformations 

 analogous to that of benzoic acid into hippuric acid, since like it they unite 

 to a greater or less extent with glycocoll. The acids thus formed have been 

 designated as salicyluric, oxyberizuric, paroxybenzuric, etc. 

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