PUBIN BASES. 345 



yeast auto-digestions that hypoxanthin and xanthin are readily de- 

 stroyed by the action of the enzyme whereas adenin and guanin resist. 

 The xanthin derivatives however have been studied carefully and 

 the results are extremely interesting. Thus, the caffein and theo- 

 bromin of the food are progressively broken up into simpler xanthin 

 bodies and a large part of the xanthin molecule is completely de- 

 stroyed. The cleavage of caffein will be described in detail later but 

 in this connection it is desirable to point out that most of the purin 

 bases found in the urine owe their origin not to direct tissue met- 

 abolism but rather to the cleavage of caffein and similar bases 

 introduced with the food. Inasmuch as the increase of purin bases 

 is not proportional to the amount of caffein ingested it is evident 

 that considerable of the latter is destroyed. Moreover it may be 

 considered as an established fact that caffein does not increase the 

 amount of uric acid although the use of coffee according to Taylor 

 is followed by a marked increase in the elimination of this product. 



The pharmacological action of the purin derivatives has been re- 

 cently (1901) investigated by Schmiedeberg. Owing to the extremely 

 slight solubility of some of these bases it follows that their effects 

 are but slight. In general the well known effects of caffein are re- 

 produced, although obviously differences exist. The action of caffein 

 is directed upon the central nervous system, the muscles and the 

 kidneys. The effects on the former are seen in the increased reflex 

 irritability which, as in the case of strychnin, may lead to complete 

 tetanus and even paralysis. The muscles contract more easily and 

 more effectively and with large doses they become permanently con- 

 tracted, passing into a condition of coagulation like that caused by 

 heat and cold (see Cushny's Pharmacology). The action on the kid- 

 ney is seen in the marked diuresis. 



Purin exerts a slower coagulation effect upon muscles and causes 

 increased reflex irritability. The resemblance to caffein is even more 

 marked with methyl purin. 



Hypoxanthin was found to have no action upon muscle, but the 

 effect upon the nervous system was seen in the increased irritability 

 and tetanus. The di-methyl hypoxanthin had a slight action upon 

 the muscles and also tetanized. On the other hand 8-oxypurin, the 

 isomer of hypoxanthin, did coagulate muscle, but showed no tetanic 

 action, whereas its di-methyl derivative showed both effects and was 

 about as active as theobromin. 



Xanthin agrees in its action fully with the above 8-oxypurin ; 

 that is it causes muscular rigor and general paralysis, but no 

 increased irritability. The alkyl derivatives of xanthin cause 

 greater rigor of the muscles and otherwise act like caffein and 

 theobromin. Of the di-methyl xanthins theobromin showed less 

 action on muscles than theophyllin, while paraxanthin was the most 

 active. 



