1867.] 



Fatty Acid from Urine. 



139 



These experiments lead to tlie conclusion that human urine contains in 

 a state of solution a crystalline fatty acid, having the general properties of 

 the members of this class, which are solid at the ordinary temperature. 

 The quantity of this substance which I obtained was too inconsiderable to 

 enable me to determine its composition, and the melting-point therefore 

 alforded the only means of ascertaining whether it is identical with any of 

 the known fatty acids or not. "Were it not for the low melting-point there 

 would be nothing to oppose the conclusion that it is palmitic acid, one of the 

 constituents of human fat. It is, however, a well-known fact that mixtures 

 of two solid fatty acids in certain proportions melt at a lower temperature 

 than the most fusible even of the constituents. For instance, according 

 to Heintz, a mixture of 30 parts of stearic acid with 70 of palmitic acid 

 fuses at 55°" 1 C, though the melting-point of the former when pure is 

 70° and of the latter 60°. This urinary acid may therefore be a mixture 

 of this kind and not a peculiar substance — in fact a mixture of tlie two 

 acids just named, which, according to recent investigations, constitute 

 together what was formerly called margaric acid, the solid acid of human 

 fat. 



Considering how many of the organs and secretions of the human body 

 contain fat, it need not excite surprise that a minute quantity of fatty acid 

 should be found in urine also, in consequence of deficient oxidation or 

 from other causes. That it forms a normal constituent of the secretion 

 I do not venture to assert, though the urine employed in my experiments 

 in no case exliibited anything peculiar, and when submitted to the process 

 above described, never failed to yield a little of the fatty acid. The quan- 

 tity obtained was always extremely small. In one experiment, for instance, 

 45 litres of urine yielded 0*14 grm. of tolerably pure acid, which, assuming 

 the urine to have been of average composition, would be equal to the 

 22000th part of its solid constituents. It is far from certain, however, that 

 this was the total quantity contained in it. The sim^ple method of sepa- 

 rating the substance from ttie urine which I have described will enable 

 pathologists to determine whether in cases of disease its quantity is sensibly 

 increased. 



The question how this fatty acid, which belongs to a class of bodies 

 alm.ost insoluble in water, comes to be dissolved in urine will naturally 

 suggest itself, but it is one to which it is difficult to find a satisfactory reply. 

 Whether urine is capable of dissolving a small quantity of the acid itself, 

 whether the latter is contained in it in combination with some base, the 

 compound being soluble in water but not decomposable by the weak acids 

 of the urine, or whether, as there seems reason to suspect, the extractive 

 matters promote the solubility of the fatty acid in water, are points on 

 which I express no opinion. That the animal charcoal, when used in 

 the manner above described, effects not a mere filtration, but an actual 

 separation of some of the constituents of urine, may be considered as quite 

 certain. 



L 2 



