[31] The details of this arrangement are founded solely upon the _therapeutic operation_ of medicines, as used to cure diseases, and not in any way upon their _physiological action_ upon a healthy man. Much unnecessary confusion, in works on Materia Medica, has arisen from these two different matters being taken into account at the same time. Food is the only restoration of wanting material needful to a healthy man; neither is there in such a case any need or opportunity for the counteraction of morbid agencies. [32] Animal Chemistry, p. 20. [33] Possibly some parts of the bile, besides the colouring matter, are truly excrementitious. But part of it is needful in the animal economy, as has been proved by experiment. M. Schwann found that when the contents of the bile-duct in dogs were caused to discharge themselves externally through a fistulous opening in the wall of the abdomen, the animals quickly wasted away and died. In some cases of jaundice, the constituents of the bile appear to be vicariously excreted by the kidneys; and perhaps the great depression produced by that disorder maybe partly accounted for by the impossibility of the re-absorption into the blood of these substances, naturally formed by the liver. Having passed into the urine, there is no provision to enable them to return. [34] He states that one equivalent of binoxalate of ammonia and four of water contain together the same elements as an atom of Taurine. (_Vide Simon's Animal Chemistry_, vol. i. p. 47. _Syd. Society._) [35] A deposit of Oxalate of Lime occurs sometimes. It is seen in minute octahedra; but is rarely in sufficient quantity to be distinguished by chemical tests. It does not come within the influence of Solvent medicines. [36] Some suppose that this acid occurs in healthy urine is a free state. It is more commonly thought to exist as Urate of Ammonia. Lehmann states that it is found as Urate of Soda. Others imagine that it is held in solution by means of Phosphate of Soda. [37] This acid is ascribed by some to Urate of Ammonia, which is to a small extent soluble in water. Others consider that it is due both to this and to Phosphoric acid, which is the opinion of Dr. Prout and Dr. G. Bird. Others attribute it to Lactic acid, which is stated by Berzelius, Lehmann, and Simon, to exist in healthy urine. Some consider the acid to consist in a Super-phosphate of Soda. Liebig supposes that it is due to Uric acid, held in solution by the common Phosphate of Soda. He also considers Hippuric acid to be an invariable ingredient in healthy human urine. [38] According to Simon it is 1.0125; Becquerel makes it 1.017; Dr. Prout and Dr. Golding Bird, 1.020; Berzelius rates it still higher.