384 



EXCRETION BY THE SKIN AND KIDNEYS. 



after it has been taken with vegetable food or with certain medicinal sub- 

 stances. The ordinary rhubarb, or pie-plant, contains a large quantity of cal- 

 cium oxalate, which, when th'is article is taken, will pass into the urine. It 

 is probable, however, that a certain quantity may be formed in the organism. 



Inasmuch as pathological facts have shown pretty conclusively that oxalic 

 acid may appear in the system without having been introduced with the food, 

 some physiologists have endeavored to show how it may originate from a 

 change in certain other substances from which it can be produced artifi- 

 cially out of the body. One of the substances from which oxalic acid can be 

 thus formed is uric acid. Woehler and Frerichs injected into the jugular 

 vein of a dog a solution containing about twenty-three grains (1*5 gramme) 

 of ammonium urate. In the urine taken a short time after, there was no 

 deposit of uric acid, but there appeared a large number of crystals of calcium 

 oxalate. The same result followed in the human subject, on the adminis- 

 tration of sixty-seven grains (4-34 grammes) of ammonium urate by the 

 mouth. These questions have more pathological than physiological impor- 

 tance ; for the quantity of calcium oxalate in the normal urine is insig- 

 nificant, and this salt does not seem to be connected with any of the well 

 known processes of disassimilation. 



Xanthine, Hypoxantliine, Leucine, Tyrosine and Taurine. Traces of 

 xanthine (CsH^N^Og) have been found in the normal human urine, but its pro- 



Fio. 127. Crystals of tyrosine (Funke). 



FIG. 128. Crystals of taurine (Funke). 



portion has not been estimated, and observers are as yet but imperfectly 

 acquainted with its physiological relations. It has been found in the liver, 

 spleen, thymus, pancreas, muscles and brain. It is insoluble in water but is 

 soluble in both acid and alkaline fluids. Hypoxanthine (0 5 H 4 N 4 0) has never 

 been found in normal urine, although it exists in the muscles, liver, spleen and 

 thymus. Leucine (C 6 H 13 N0 2 ) exists in the pancreas, salivary glands, thyroid, 

 thymus, suprarenal capsules, lymphatic glands, liver, lungs, kidneys and the 

 gray substance of the brain. It has never been detected in the normal urine. 

 The same remarks apply to tyrosine (CaHnNOs), although it is not so exten- 

 sively distributed in the economy, to taurine (C 2 H 7 N0 3 S) and to cystine 



