" I have convinced myself, by careful and minute examinations, that urine emitted after drinking a copious amount of water invariably contains a somewhat larger amount of salts than the water which has been drank ; whilst the amount of phosphates contained in the last emitted portions of the urine is extremely minute, and no longer detectable by the ordi nary tests. It is, therefore, obvious that all the salts, without exception, contained in the urine, are to be considered as accidental con stituents of the blood, which are excreted and removed from the organism precisely because they no longer form part of the normal consti tution of the blood. The phosphates emitted with the urine were, previously, constituent substances which have been decomposed in the vital processes, or they existed as consti tuents of the blood, but upon its transforma tion into living tissues they were not admitted into their composition, they were not required in the constitution of the latter.
" Now, among the products of the vital processes, which, together with the soluble phosphates, are removed from the organism through the urinary organs and channels, there are two organic acids, namely, uric acid and hippurie acid, both possessing the property of combining with the soda or potass of the alkaline phosphates, and acquiring in the com bination a higher degree of solubility than they possess, per se, at the common temperature of the body. It is obvious that, by the accession of these two acids, and by their action upon the phosphates of soda, an urate and hippurate of soda must be formed on the one hand, and an acid phosphate of soda on the other ; and that, consequently, the urine must acquire an acid reaction.
" But the presence of these two acids in the urine is not the only cause of its acid nature , there exists another cause, which tends pow erfully to maintain and increase it.
" According to the preceding remarks we ought to find in the urine all the soluble salts of the food, as well as a small amount of the phosphate of lime, which is soluble to a cer tain extent in acid fluids, together with mag nesia. The amount of these latter substances will be in proportion to their solubility in acid phosphate of soda. The other insoluble salts of the aliments we ought to find in the faeces. In other words, assuming that the materials composing the aliments become converted into oxygen compounds, that is, are burnt in the organism, we ought to find in the urine all the soluble salts of their ashes, and in the faeces all the insoluble salts. Now, upon comparing the constitution of the ashes of the blood or of the aliments, or, rather, the salts contained therein, with those contained in the urine, we find that there exists a striking difference be tween their respective amounts of sulphates.
" According to the analyses of the ashes of the grains of wheat and rye*, the urine of an individual feeding exclusively upon bread ought not to contain a single trace of a sul phate, whilst the urine of an animal fed upon peas or beans ought to contain sulphates toge ther with phosphates, in the proportion of nine of the former to sixty of the latter. Finally,
as flesh contains no soluble alkaline sulphate (broth does not yield any precipitate of sulphate of barytes when tested with salts of barytes), the urine of carnivorous animals ought to be equally free from soluble sul phates. We find, on the contrary, that the urine of man, according to the most correct analyses, contains a far larger proportion of sulphates than the aliments partaken of; nay, even that the amount of the sulphuric acid received into the system must, in many cases, be equal or superior to that of the phosphoric acid contained in the aliments. According to the analysis of human urine made by Berze lius and Lehmann, the amount of the sul phates present in urine is nearly double that of all the soluble phosphates together. Hie ronymi found the amount of sulphate of potass contained in the urine of the tiger, the lion, and the leopard, compared with that of the phosphates, to be as 1 to 7. It can be distinctly and positively proved that these salts have not been partaken of in such pro portions. But we now know the origin of the greatest portion of the sulphuric acid con tained in the urine; this acid has entered the organism with the food, not in the form of a sulphate, but as sulphur.
" Gluten*, vegetable casein, flesh, albumen, fibrin, and the cartilages and bones, contain sulphur in a form quite different from the oxygen compounds of this substance. This sulphur is separated as sulphuretted hydrogen during the putrefaction of these substances ; it combines with the alkalies, operating upon these animal substances, and may be ob tained from such combinations in the form of sulphuretted hydrogen by means of stronger acids.
" Now, we know from the experiments of Willer, that the soluble sulphurets become oxidised in the organism ; and that thus, for instance, sulphuret of potassium becomes con verted into sulphate of potass ; and it is there fore unquestionable that the sulphur of the constituents of the blood, derived from the aliments, or, what comes to the same point, the sulphur of the transformed tissues be comes finally converted into sulphuric acid by the oxygen absorbed in the process of respiration, and thus that in the urine it must appear in the form of sulphates ; and from this cause the original amount of these salts contained in the aliments becomes increased. The alkaline base which we find in the urine, in combination with this sulphuric acid, is supplied by the soluble alkaline phosphates ; and the latter, in consequence of the loss of part of this base, are converted into acid salts.