THE ELIMINATION OE CAEFEIN. 21 



SUMMARY AND CONCLUSIONS. 



Caffein administered subcutaneously, by mouth, or intravenously 

 is eliminated in part unchanged, in the urine, into the gastrointes- 

 tinal canal, and into the bile. The amounts recovered in the urine 

 of rabbits varied from 1.72 to 14.02 per cent of the quantity intro- 

 duced into the body. In most cases it was approximately 6 to 10 

 per cent. More caffein was eliminated on a diet of carrots than on 

 oats or hay, which is probably due in part to the increased diuresis 

 when carrots are eaten. The elimination of caffein in the guinea pig 

 was found to be between 6 and 11 per cent. As in the rabbit, more 

 caffein was found in the urine of carrot-fed subjects as compared 

 with the oat fed. The elimination into the gastrointestinal canal 

 was found to be marked in the guinea pigs as well as in rabbits. In 

 both cases more caffein was found when oats were fed than when a 

 diet of carrots was given. The presence of very small quantities of 

 caffein in the gastrointestinal contents of animals at the end of forty- 

 eight hours points to its reabsorption into the circulation, since de- 

 struction of caffein is highly improbable on account of its resistance to 

 bacterial action. 



Cats and dogs eliminated very small quantities, slightly over 1 per 

 cent of the amount ingested. The elimination of caffein begins soon 

 after its introduction into the circulation. It was found in the urine 

 from fifteen to forty minutes after its subcutaneous injection and in 

 some cases continued to be present for forty-eight hours. The greater 

 part, however, is eliminated during the first twenty-four hours, only 

 small quantities being found in the urine later. 



The data herein presented lead to the conclusion that in the carni- 

 vora larger amounts of caffein are demethylated than in the herbivora, 

 and that the resistance to caffein is inversely as demethylation, since 

 it has been shown that caffein is much more toxic for carnivora than 

 for herbivora. The mechanism of demethylation is in all probability 

 utilized in the body as a means of defense against the deleterious action 

 of caffein, being more active in organisms for which the drug is more 

 toxic. 



