ITS NORMAL CHEMICAL CONSTITUENTS. 399 



We now pass to the non-organic formations of chemical sub- 

 stances which occur in the urine, and which give rise to the urinary 

 sediments when present in large quantities; amongst these the or- 

 dinary amorphous urate of soda occupies the principal place. We 

 have already noticed this substance at length, at p. 214 of vol i., 

 where we also referred to the occurrence of urate of ammonia) in the 

 form of dark globular molecules studded with fine needles, in urine 

 that has become alkaline. 



The prismatic crystals of the phosphate of ammonia and 

 magnesia occur only in neutral or alkaline urine ; this substance 

 was also noticed at p. 424 of vol. i. 



The octohedral crystals of oxalate of lime, which are found in 

 small quantities in the normal urine, and in greater abundance in 

 certain morbid conditions, have also been described in vol. i., pp. 

 4347. 



The crystals of cystine, described in vol. i., p. 178, constitute a 

 less frequent spontaneous sediment of morbid urine. 



Urea occupies the first place amongst the chemical consti- 

 tuents of the urine, both because it exceeds in quantity all the 

 other solid constituents of this fluid, and on account of the 

 important part which this body plays amongst the detritus of 

 the metamorphoses of animal matter, both in a physiological 

 and in a chemical point of view. All these relations have already 

 been fully considered in vol. i., pp. 153 168. 



A similar observation may be made in reference to the uric 

 acid present in the urine (vol. i., pp. 199 220.) 



We have already stated in our description of the chemical and 

 physiological relations of hippuric acid (see vol. i., pp. 188 199), 

 that this acid must be regarded as a normal constituent of human 

 urine. 



Liebig's discovery that the nitrogenous and crystallizable 

 bodies, known as creatine and creatinine, which are contained in 

 the fluid of the flesh, also occur in the urine, induced us to enter 

 into a full consideration of these substances in the first volume. 

 (See pp. 134142.) 



We have already spoken in vol. i., p. 99, of the occasional 

 presence of lactic acid and lactates. 



We treated at pp. 318321, vol. i., with all possible brevity, of 

 the extractive and colouring matters of the urine ; and as it would 

 only lead to confusion, if we were to notice the numerous and 

 fruitless observations which have been made on this subject, we 

 will leave this question for the present, in the hope that it may 



