THE TOXICITY OF CAFFEIN. 



INTRODUCTION. 



Comparative physiology has established the fundamental fact that 

 some properties are common to all forms of living matter. But the 

 same method of inquiry has also led to the recognition of marked 

 differences in the physiological processes of various species of animals. 

 Among the most important investigations which contributed to the 

 knowledge of such variation of function are the studies in comparative 

 metabolism. It is now recognized that metabolism is in some 

 respects quite different in herbivora and in carnivora. Some forms 

 of oxidation are much greater in the rabbit than in cats and dogs. 

 Nuclein metabolism presents important differences in the rabbit and in 

 man, while the mode of neutralizing acid in the body may be cited as 

 another variation in the metabolism of these forms. Perhaps the 

 most striking examples of differences in the metabolism of different 

 organisms is furnished by the results of studies on the fate of certain 

 poisons introduced into the body. 



The classical experiments of Bunge and Schmiedeberg 15 a on the syn- 

 thesis of hippuric acid are of interest in this -regard. It will be recalled 

 that in the dog the synthesis takes place in the kidney ; the rabbit is able 

 to form hippuric acid in the liver as well as in the kidney, while frogs 

 can synthesize hippuric acid even when both of these organs have been 

 removed or excluded from the circulation. Observations on the fate 

 of some of the alcohols of the fatty acid series have likewise shown that 

 these substances maybe combined with glycuroni* acid in some animals 

 but not in others. According to Thierfelder and Von Mering, 84 ter- 

 tiary alcohols are combined in this manner in the rabbit but not in the 

 dog. According to Nsubauer, 64 the primary and secondary alcohols 

 are so combined in the dog as well as in the rabbit, but to a greater 

 degree in the latter. 



Pohl 73 found that amyl alcohol is largely eliminated by the lungs in 

 the cat and in the dog. The protocols of his experiments show that 

 65 per cent of the alcohol given these animals was thus recovered, 

 while he recovered only 22 per cent of this substance in the expired 

 air of the rabbit. Examination of tne urine showed the presence of 

 glycuronic acid. Hofmeister's 37 work with tellurium in the dog is of 



o The small figures refer to the bibliography at the end of this bulletin. 



