54 MATERIAL COMPOSITION OF MAN. 



and is one of the constant products of the putrid fermentation of ani- 

 mal or vegetable substances. It is the most prevalent of the vegetable 

 acids, and most easily formed artificially. 



4. Oxalic acid. This acid, which exists extensively in the vege- 

 table kingdom, but always united with lime, potassa, soda, or oxide of 

 iron, is only found, combined with lime, as an animal constituent in 

 certain urinary calculi. 



5. Benzoic acid. This acid, found in many individuals of the vege- 

 table kingdom, is likewise met with in the urine of the horse, cow, 

 camel, and rhinoceros ; and sometimes in that of man, especially of 

 children. When benzoic acid is swallowed, hippuric acid is observed 

 in the urine ; and it was supposed by Mr. A. Ure and others, that this 

 was owing to the conversion of uric acid into hippuric ; and as the 

 hippurates are more soluble, it was suggested by him, that benzoic acid 

 might be advantageously exhibited in lithuria, and in cases of gouty 

 depositions of lithate of soda. It has been found, however, by Drs. 

 Keller and Garrod, 1 and by Professor Booth, and Mr. Boyd, of Phila- 

 delphia, 2 that the administration of benzoic acid exerts no influence on 

 the amount of uric acid in the urine. 



6. Lactic acid. Acid of milk is met with in blood, gastric juice, 

 urine, milk, marrow, and also in muscular flesh. At times it is in a 

 free state, but is usually united with alkalies. However much it may 

 be concentrated, it does not crystallize, but remains under the form of 

 syrup or extract. When cold it is tasteless, but when heated has a 

 sharp acid taste. According to Dr. Prout, this acid, like urea, results 

 from the decomposition of the gelatinous parts of the system ; accord- 

 ing to Berzelius, however, it is a general product of the spontaneous 

 decomposition of animal matters within the body. Liebig 3 formerly 

 denied, that any lactic acid is formed in the stomach in health ; and 

 affirmed, that the property possessed by many substances, such as starch, 

 and the varieties of sugar, by contact with animal matters in a state 

 of decomposition, of passing into lactic acid, had induced physiologists 

 too hastily to assume the fact of the production of lactic acid during 

 healthy digestion : yet he now admits its presence. 



7. Sugar of milk. This substance, which is so called because it has 

 a saccharine taste, and exists chiefly, if not solely, in milk, differs from 

 ordinary sugar in not fermenting. It is obtained by evaporating whey, 

 formed during the making of cheese, to the consistence of honey; al- 

 lowing the mass to cool ; dissolving ; clarifying and crystallizing. It 

 commonly crystallizes in regular parallelopipedons, terminated by pyra- 

 mids with four faces. It is white ; semitransparent ; hard, and of a 

 slightly saccharine taste. 



8. Sugar of diabetes. In diabetes meltitus, the urine, which is often 

 passed in enormous quantity, contains, at the expense of the economy, 

 a large amount of peculiar saccharine matter, which, when properly 

 purified, appears identical in properties and composition with vegetable 



1 Liebig's Animal Chemistry, p. 316. 



a Proceedings of the American Philosophical Society at the Centennial Celebration in Phila., 

 May, 1843, and Transactions of the A. P. Society, vol. ix. pt. 2, Philad., 1845. 

 3 Op. cit., p. 107. 



