532 Chemical Physiology and Pathology. 



obviously owe their origin to the culinary salt used at meals, 

 the soda of which plays an important part in the reduction 

 of food, containing fibrine and caseine along with albumen, 

 and in the formation of bile, which is a sort of soap-like com- 

 pound. This free acid plays a similar part to sulphuric acid, 

 which in a mixture of diastase and amyline hastens their meta- 

 morphosis into sugar. In truth we know nothing more re- 

 garding digestion, except the outward essentials to its taking 

 place ; the particular histories of the substances broken down 

 by the transformation are, for the greater part, unknown. 

 Liebig has, by a comparison of the final chemical results of 

 the transformation with the commencement of the process, 

 (that is, of the substances taken in and those evacuated) made 

 a first step towards dispelling this darkness. Urine contains 

 the products of the transformed structures which are richest 

 in nitrogen, bile of those which are richest in carbon ; and 

 as all structures have originally been produced by the blood, 

 so must the elementary constituents of the bile and urine 

 taken together, resemble the composition of the blood, in 

 their relative proportions. But in the transformation of 

 structures, no other bodies except the oxygen of the air and 

 water have taken part: we must therefore find again all the 

 constituents of blood in the constituents of urine and bile, 

 with the addition of a certain quantity of oxygen and of water ; 

 and we find that choleic acid represents the bile, uric acid 

 and ammonia the elements of urine. If then we abstract 

 from the composition of blood the constituents of urine, we 

 must after making allowance for the quantity of oxygen and 

 of water which has been added, arrive at the composition of 

 bile. Or vice versa, after abstracting the constituents of 

 bile with oxygen and water, from the constituents of the 

 blood, we must arrive at urate of ammonia, or urea and car- 

 bonic acid. As the last products of these transforma- 

 tions we obtain, (because the choleic acid is reduced into 

 carbonic acid and the uric into carbonic acid, and ammonia) 



