10 THE ROYAL SOCIETY OF CANADA 



than 93, may sink as low as the neighbourhood of 70. To this type 

 conform the marsupialia and the proboscidea, as exempHfied respect- 

 ively by the opossum and the elephant, and also certain ungulates, 

 such as the cow and the horse. 



(3) A type in which, while the power to destroy uric acid is 

 apparently as high as in the first, the bases exceed appreciably that 

 substance in quantity. The only known representative of this type 

 is the pig. 



(4) The fourth type resembles the third in the excess of bases 

 over uric acid, but differs from it in having the uricolytic index com- 

 paratively low. The guenon monkey among primates, and the sheep 

 and goat among ungulates, are examples. 



(5) Man and the chimpanzee (possibly of course the other anthro- 

 poids) form a class by themselves, characterized by the practically 

 entire absence of uricolytic power, and the consequent replacement, 

 as end product of purine metabolism, of allantoin by uric acid. 



As far as our personal observations go, the individuals of a 

 species not only conform to a single type, but vary to a very limited 

 extent within it. It would nevertheless be an error to convert this 

 experience into a generalization. Wiechowski^ has reported observa- 

 tions upon two horses, from which one may calculate uricolytic indices, 

 50 and 79 respectively, that are decidedly lower than our estimate 

 of 88; and according to Schittenhelm and Bendix- the ratio of bases 

 to uric acid in horses' urine may be as high as 8 to 1, although the 

 horses coming under our observation excreted hardly any purine 

 bases whatever. A still more striking instance of variability within 

 the species has recently been reported by Benedict.^ The Dalmatian 

 coach dog, as he discovered, differs from other dogs in excreting a 

 decidedly higher proportion of uric acid than of allantoin, so that its 

 purine metabolism actually approaches the human type more than 

 that of any other mammal lower in the scale than the chimpanzee. 

 It appears therefore that, although as a general rule each species 

 maintains a characteristic type of purine metabolism, special circum- 

 stances (among which domestication possibly plays an important 

 part) may induce divergences peculiar to a particular race or breed. 

 This possibility has an obvious bearing upon the problem of the 

 evolutionary development of the different types. 



On passing from the species to the order somewhat similar rela- 

 tions are encountered. No positively significant difference exists 



^ Wiechowski: Biochem. Z., xix, p. 368, 1909. 



2 Schittenhelm and Bendix: Z. physiol. Chem., xlviii, p. 140, 1906. 



' Benedict, S. R.: J. Lab. and Clin. Med., ii, p. 1, 1916. 



