1864.] Dr. Marcet on a Colloid Acid of Urine. 9 



urine 4'46 grammes of the colloid acid. This is probably hardly half the 

 quantity contained in that bulk of the secretion. I have some reason to 

 believe that the colloid acid described in this paper is not confined to the 

 urinary fluid, but is found elsewhere in the human body ; indeed its secre- 

 tion by the kidneys shows that it very probably exists in the blood. My 

 experiments on the blood have not yet been carried far enough to enable 

 me to communicate the results obtained from this inquiry. 



The functions of the colloid acid of urine while in the blood, assuming 

 that it enters into its composition, must be very important. There can be 

 little doubt that it is intimately connected with the secretion of gastric 

 juice, by displacing the hydrochloric acid of the chloride of sodium in the 

 blood, and transforming the soda into a colloid salt, which, from its colloid 

 nature, would be retained in the blood, while the free hydrochloric acid 

 would pass into the stomach to form gastric juice. I have undertaken an 

 experiment in connexion with this point, which showed that, after dialyzing 

 for five hours a mixture of chloride of sodium and of the colloid acid of 

 urine, the hydrochloric acid had nearly entirely passed through the dialyzer, 

 while rather less than half the amount of the colloid acid had remained on 

 the diaphragm, holding some soda, though a small quantity, in solution ; 

 from an accidental omission in my notes, I regret being prevented from 

 giving the details of the experiment. 



The free colloid acid being capable to a certain extent of passing through 

 a membrane, its secretion by the kidneys, urine being generally acid, is 

 easily accounted for. 



As to the mode of formation of the colloid acid of urine in the human 

 body, we have, so far, no positive knowledge. From its composition and 

 colloid nature, it may probably be derived from some transformation of the 

 colloid non-nitrogenous product of the liver, known as the glucogenic 

 substance. 



Neubauer and Vogel's book on urine contains an account of the mode of 

 preparation and characters of four organic acids discovered in this secretion 

 by Stadeler, these substances being phenylic, taurylic, damaluric and 

 damolic acid. They are obtained from urine by distillation, and are 

 crystalloids, and therefore can have no relation to the substance I have 

 described in this paper. 



When better acquainted with the chemical composition and physio- 

 logical relations of the colloid acid of urine, I shall be able to give it an 

 appropriate name. 



