INTERMEDIATE OXIDATION PRODUCTS. 1 09 



such as amido-valeric acid or phocine, hexacarbon compounds 

 such as amido-caproic acid or leucine, and heptacarbon com- 

 pounds such as the benzoic residue of hippuric acid, and the 

 salicic residue of tyrosine. 



(i 16.) You will remember that by certain processes of artifi- 

 cial oxidation to which I referred in a former lecture, we obtain 

 from any particular substance a series of less and less complex 

 bodies terminating in carbonic acid ; or, to use again the words 

 of Gerhardt, we gradually descend the scale of complexity, con- 

 verting the original substance into more and more simple products 

 by successively burning off a portion of its carbon and hydrogen. 

 In other cases, however, as in some of Gorup-Besanez's experiments 

 upon the oxidation effected by ozone in alkaline liquids, whether or 

 not a series of bodies intermediate between the initial substance 

 and final carbonic acid are really formed, we are quite incapable of 

 detecting them, and consequently, of tracing their metamorphoses. 

 The constituent carbon-atoms of the original substance seem, at 

 any rate, to become at one step completely isolated and oxidised. 

 Whether, therefore, the more complex molecules formed by natural 

 tissue-oxidation are to be regarded as direct, but intermediate, 

 products of the principal oxidation, or as by-products resulting 

 from subsidiary processes, is at present an open question, though 

 the balance of evidence with regard to certain products, at any rate, 

 seems to be in favour of the latter view. In any case, however, the 

 formation and even excretion of some or other of these bodies, in 

 greater or less proportion, according to the nature of the organ- 

 ism, uric acid largely in birds and land-reptiles, hippuric acid 

 largely in herbivora, and both acids sparingly in mankind are 

 obviously normal or healthy actions. By the excretion of such 

 imperfectly burned substances, indeed, a certain amount of 

 force does not become utilised within the animal, but this pro- 

 digality of force in organic nature is far inferior to that which 

 we observe in the inorganic world. Some of these inter- 

 mediate products of tissue metamorphosis, more particularly 

 the hippuric and uric acids, leucine and tyrosine, are of suffi- 

 ciently constant occurrence and general interest to deserve our 



