ANIMAL OXIDATIONS. 453 



are merely cited to show that the oxidation processes taking place in the 

 animal organism are by no means to be considered as direct in nature, i.e., 

 the cleavage-products as such (the amino acids, dextrose and the fatty 

 acids), are of themselves not susceptible to oxidation in the tissues under 

 the prevailing conditions, unless it be assumed that, for example, d-leucine 

 does not enter into the metabolism of the cells and does not come in con- 

 tact with the carriers of oxygen. There is, however, no support to such 

 an assumption. On the contrary, we know that the muscular cells of the 

 diabetic are constantly being offered d-glucose. The cells consume albu- 

 min and fat, or rather their decomposition products, just as well as ever. 

 Glucose alone they allow to pass on unchanged. The key is lost which 

 can unlock the energy stored up in the glucose molecule. Now of course 

 an assumption that the oxydase which is capable of offering oxygen to the 

 dextrose is absent, helps us here. The fact that the diabetic can complete 

 the oxidation without difficulty, if the glucose is previously converted 

 into a more readily oxidizable form, does not necessarily prove, however, 

 that the glucose molecule must be opened up in some way before oxida- 

 tion. It is indeed possible that the glucuronic acid and saccharic acid 

 offered to the diabetic may be consumed at an entirely different place in 

 the organism, and not utilized at all for the work of the muscular cells. 1 

 At the same time the empirical knowledge that we possess, indicates that 

 the foodstuffs as such are not at once suitable for oxidation. Something 

 must be taken out of the complex molecule before the oxygen in the cells 

 tissues can act upon it. The investigations of Schittenhelm point in this 

 direction. Guanine, a cleavage-product of the nucleic acids, is first of alt 

 changed into xanthine: 



HX CO HN CO HN C 



NH 2 .C C NH OC C NH OC C NH 



\ 



CH- 



\ 



CH- 



\ 



CO 



// 



N C N HN C N HN C NH 



Guanine Xanthine Uric acid 



This transformation takes place with loss of ammonia; a hydrolytic 

 ferment is active. Now for the first time the molecule is ready for oxida- 

 tion, and uric acid is formed from it. The latter is then acted upon with 

 the aid of another ferment in a manner unknown to us. We thus see that 

 a whole chain of different processes is necessary in order to completely 

 consume a relatively simple substance, a purine base. 



We must regard the breaking down of the amino acids as taking place 



1 See Lecture XIII, p. 292. 



