[hunter-ward] purine METABOLISiM 11 



between the various species of rodents, or the various species of 

 carnivora examined; but among primates we find represented two, 

 and among ungulates three, distinct metaboHc types. It cannot 

 therefore be said for the order, any more than for the species, that its 

 purine metaboHsm invariably presents the same, or even similar 

 characteristics. It 'is again perhaps not without importance that the 

 order presenting in this respect the greatest variety is that which has 

 been, in the examples available, the most subject to the selective 

 operations of the breeder. 



Viewing the collected results from the standpoint of phylogeny, 

 we have to admit that they do not as yet reveal any continuous line of 

 development from one type to another. The most that can be said is 

 that, though totally dissimilar groups, such as rodents and carnivora, 

 may present almost identical metabolic habits, widely divergent types 

 arise for the most part in remotely related orders. Even this limited 

 generalization has exceptions, as may be seen by comparing the pig 

 with the horse, or the monkey with the chimpanzee. The second 

 of these exceptions points, as it happens, to the most interesting 

 single fact discovered in this connection, namely, that the primates 

 nearest to man have already acquired his peculiar type of purine 

 catabolism; but between these and the lower primates there still 

 exists a gap as great almost as that which separates man from the dog. 

 Evidently the history of the evolution of purine metabolism among 

 mammals, if it should ever be possible to write it, demands as its 

 basis a much more extensive material than we yet possess. 



We take pleasure in acknowledging the courtesy of Mr. R. C. 

 Harris, Acting Commissioner of Parks, City of Toronto, and Mr. F. 

 Goode, formerly Superintendent of the Riverdale Zoo, in facilitating, 

 by the loan of animals and otherwise, the progress of this investigation. 



