Chemical Changes in Animal Organism. 301 



and galactose. This ferment is absent, or present only in 

 small quantities, in the intestines of adult animals, which 

 draw their carbohydrate supply from sources other than 

 that of the milk. 



A large number of ferments exist in the liver, and 

 have been the subjects of numerous investigations. 



So far the enzymes affecting the hydrolysis of fats, 

 carbohydrates, and proteins have been discussed. There 

 exist in the organs, however, another very important 

 class, namely, those to which the oxidative processes in 

 these organs are due. These are known as the oxydases, 

 and a very large number probably exist. Much remains 

 to be learnt about these ferments ; as examples, the in- 

 vestigations dealing with the degradation products of 

 nucleic acid may be cited. As already stated, much atten- 

 tion has been directed towards the study of the meta- 

 bolism of this acid, in view of the important part it 

 appears to play in certain pathological conditions (p. 284). 

 It may be recalled that it yields on hydrolysis certain 

 purine bases which are closely related chemically to uric 

 acid. This is evident from the formulae given below 



HN-CO HN CO HN CO 



HC C NH > OC C-NH * OC C NH 



>CH 



>CH 



_L 



N C N HN C N HN C NH 



Hypoxanthine. Xanthine. Uric Acid. 



It will be noticed that it is possible to pass from 

 hypoxanthine through xan thine to uric acid. Numerous 

 investigations have been carried out with the object of 

 ascertaining which organs of the body produce these 

 oxidative changes, and which organs also cause the oxida- 

 tive destruction of uric acid itself. It has been found 



