EXCREMENTITIOUS SUBSTANCES. 91 



be inferred that these acids do not originally exist in the fluid, but that they 

 are formed there by a fermentation-process subsequently to its removal from 

 the body. The recent discovery of Inosite, or muscle-sugar ( 46), appears 

 to afford a connecting link by which we may account for the production of 

 lactic acid in this situation. 



63. It will the better serve to show the remarkable predominance of Nitrogen 

 in nearly all of these excrementitious matters now described, if we arrange their 

 respective formulae in a tabular mode, and compare the percentages of that ele- 

 ment which they severally contain. 



Percentage 

 Carbon. Hydrogen. Nitrogen. Oxygen, of Nitrogen. 



49 36 6 14 W 7 



40 31 5 12 } 15 ' 67 



2 4 2 2 46.67 



5223 33.33 



18 9 1 6 7.82 



10 7 2 11 15.30 



8546 35.44 



8934 32.06 



8732 37.17 



Urea 



Uric Acid 



Hippuric Acid (hydrated' 



Inosic Acid (hydrated) 



Allantoine (hydrated) 



Creatine 



Creatinine 



Thus we see that whilst the proportion of nitrogen in Inosic acid is almost pre- 

 cisely the same as in Albumen, the proportion of nitrogen in Uric acid, Allan- 

 toine, Creatine, and Creatinine, is more than double that which Albumen contains, 

 whilst that of Urea is almost exactly triple ; on the other hand, the percentage 

 of nitrogen in Hippuric acid is exactly half that which is found in Albumen. 

 Again, the percentage of carbon in Hippuric acid (60.33) considerably exceeds 

 that which Albumen contains (54.88), and is no less than three times as great 

 as that which exists in Urea (20.0). 



64. Before quitting these characteristic components of the Urinary secretion, 

 it will be desirable to mention certain other organic substances, of which some 

 are constantly present in it, whilst the occurrence of others is exceptional or 

 abnormal. Chemists have been in the habit of designating, under the general 

 term Extractive Matters, substances which, whether they are produced by the 

 reagents employed, or exist preformed in the animal fluids, are so deficient in 

 characteristic properties, that they are not capable of being distinguished by 

 analytical processes, or of being separated and exhibited in a pure state. With 

 the progress of science, however, one substance after another has been with- 

 drawn from this group ; thus by the more attentive study of the extractive 

 matters of the Urine, creatine, creatinine, and hippuric acid have been found 

 among its components ; and the extractive of the Blood has already yielded 

 Mulder's binoxide and tritoxide of protein ( 30), and will probably afford 

 many more substances equally capable of being separately and characteristically 

 distinguished. The Extractive matters must therefore be regarded, according 

 to the just remark of Lehmann, as important factors in the metamorphosis of 

 animal tissue, both progressive and retrograde, and deserve the most careful 

 and attentive Chemical examination. Among the extractives of the Urine, have 

 been usually ranked the Coloring Matters; the study of which, for reasons enu- 

 merated by Lehinann (op. cit. p. 318), is attended with peculiar difficulties. It 

 was suggested by Dr. Prout that two distinct pigments probably exist ; and 

 this view is to a certain extent confirmed by the recent investigations of Scherer 1 

 and Heller. a These, however, seem to indicate that there is originally but a 

 single pigment (the uroxanthin of Heller), probably derived from the haematm 

 of disintegrated blood-corpuscles (or possibly from the pigmentary matter of 



1 "Ann. der Chem. tmd Pharm.," band Ivii. pp. 180, 195. 



2 "Arch, fur Chemie und Mikrosk.," band ii. pp. 161, 173. 



