168 THE DIGESTIVE FLUIDS. 



Taurin. As has been pointed out, taurin is not found exclusively 

 in the bile, but occurs also in the lungs, kidneys, and in the muscle- 

 tissue of many vertebrate animals. It is a derivative of cystin, 

 and thus of albuminous origin. It is noteworthy, however, that an 

 increased ingestion of albumins to eight times the usual amount in- 

 creases the biliary sulphur (taurocholic acid) only twice. This finds 

 its explanation in the observation of v. Bergmann that cystin per se 

 will not lead to an increased elimination of the bile sulphur, when fed 

 directly, while this occurs when cholalic acid is simultaneously ad- 

 ministered. AVe may accordingly conclude that under usual condi- 

 tions a sufficiently large amount of cholalic acid is not available for 

 the elimination of a larger amount of taurin than ordinary as tauro- 

 cholic acid. There is evidence that in dogs there is a store of taurin 

 (or of cystin) normally, which rapidly disappears when cholalic acid 

 is administered, as evidenced by an increased output of the bile sul- 

 phur. Personal investigations in association with Dr. D. G. Camp- 

 bell have led me to similar results in man. 



Of the manner in which cystin gives rise to taurin our knowledge 

 is not yet complete. Different possibilities exist. On the one hand, 

 the cystin may be oxidized to cystei'nic acid, which apparently 

 represents the sulpho-acid of cystei'n, and from which taurin could 

 then result through loss of CO 2 as expressed by the equations : 



CH 2 . S S. CH 2 CH 2 . S0 3 H 



CH.NH 2 CH.NH 2 + 5O + H 2 O 2CH.NH 2 



COOH COOH COOH 



Cystin Cysteinic acid 



CH 2 .SO 3 H 



.NH 2 = r-_ + C0 2 



Cysteinic acid Taurin 



| CH 2 .S0 2 .OH 



CH.NH 2 



<U 



It is possible, on the other hand, that the organism forms taurin 

 directly by oxidation of the thio- to the sulpho-group with the co- 

 incident loss of carbon dioxide. 



Then again there is a possibility that cystin may unite with chola- 

 lic acid primarily, and that the resulting product is subsequently 

 oxidized to taurocholic acid without the intermediate formation of 

 taurin. 



Unlike the loosely combined sulphur of cystin, the sulphur of 

 taurin cannot be split off on boiling with dilute alkalies. It is 

 present in oxidized form. Its separation necessitates the complete 

 destruction of the taurin. 



Wahlgreen has recently isolated the corresponding glycocholic 

 acid from ox-bile, and it is possible that this is identical with Mul- 

 der's cholonic acid : 



