URINE. 



1271 



He states its quantity as equal to that of 

 the lithic acid, in all persons feeding on a 

 mixed diet. This, however, is certainly an 

 over statement. It is present, but in small 

 proportion, in healthy urine. 



The ultimate composition of hippuric acid 

 is as follows : 



CIS, H9, Nl, O 6. 



It crystallises in four-sided prisms, obliquely 

 truncated. 



When heated it gives out an odour resem- 

 bling that of the tonqtiin bean. 



Lactic acid. The lactic acid was first dis- 

 covered in the urine by Berzelius, who ex- 

 tracted it by the following process : 



A portion of urine was evaporated to dry- 

 ness, and alcohol of specific gravity 0'833 

 boiled on the solid residuum. 



The alcoholic solution was next evaporated, 

 and the mass dissolved in water. 



The watery solution was then boiled with 

 a considerable quantity of hydrate of lime, 

 till all ammoniacal fumes (from decomposing 

 urea) were dissipated; the hydrate of lime 

 now became coloured yellow, owing to the 

 decomposition of animal matter. 



The colourless solution was filtered, dried, 

 and then treated with alcohol of specific 

 gravity '84-5. Equal parts of strong sulphuric 

 acid and water were now added, guttatim, to 

 the alcoholic solution, until sulphate of lime 

 no longer precipitated ; the clear liquor being 

 decanted was next treated with carbonate of 

 lead (recently precipitated), and was then 

 filtered and evaporated to dryness. _ 



The residue was treated with oxide of lead 

 and a little water, by which means the lactic 

 acid was converted into a sub-salt of consider- 

 able insolubility. This was collected, washed 

 with water, and then decomposed by sul- 

 phuretted hydrogen. Thus, sulphuret of lead 

 subsided, leaving the lactic acid free in the 

 supernatant liquor, which, by evaporation, 

 yielded it in the form of an acid yellow syrup, 

 exceedingly deliquescent, and incapable of 

 being thoroughly dried by heat. 



Its chemical properties are the following : 



It gives out an acrid odour * when heated, 

 and leaves a porous charcoal if the heat be 

 continued. Alcohol dissolves it in all propor- 

 tions. It is nearly insoluble in ether. 



Its salts are all of a gummy and uncrystal- 

 lisable nature, excepting the lactates of zinc 

 and magnesia, which have been obtained in a 



f5 * 



crystalline form. 



When lactic acid is added to a strong solu- 

 tion of the acetates of magnesia or oxide of 

 zinc, the lactates of those bases are pre- 

 cipitated. 



The existence of lactic acid, as a consti- 

 tuent of urine, has been denied by _ Liebig, and 

 the question is as yet far from being satisfac- 

 torily settled. 



The admission made of late by Liebig, how- 

 ever (as the result of his researches on muscle), 

 that lactic acid exists in the juice of flesh, 

 gives great probability to the correctness of 

 Berzelius's statement. 



* Not unlike that of the tartrates. 



The other constituents of the urine which 

 1 have enumerated, require no particular 

 notice in this place ; and for the methods of 

 quantitatively examining the fluid, I must 

 refer to the article ORGANIC ANALYSIS, 

 contained in this work. 



Healthy urine possesses the following phy- 

 sical characters : It is of a pale straw colour, 

 limpid and acid ; after standing some hours, 

 it deposits a light, flocculent sediment, com- 

 posed of mucus. This mucus, as it exists 

 in health, suspended in the urine, does not 

 materially interfere with the transparency of 

 the fluid. The odour of urine is peculiar, and 

 subject to modification from the use of various 

 articles of diet, and remedies. Its specific 

 gravity varies, owing principally to two causes 

 the condition of the atmosphere, as affect- 

 ing the proportion of water exhaled by the 

 skin, and the quantity and quality of the in- 

 gesta taken. 



Healthy urine may, under these considera- 

 tions, be said to vary in specific gravity from 

 1004 to 1032 ; while perhaps, under ordinary 

 or average conditions of diet, temperature, &c., 

 we may place its specific gravity at 1015 to 

 1022. 



Quantitative composition of healthy Urine. 

 The quantitative composition of urine must of 

 course vary considerably, owing to the condi- 

 tions noticed above, as affecting its specific 

 gravity. The following is the result of an 

 analysis made on 1000 parts by Berzelius, on 

 a specimen considered as healthy : 



Water 933'0 



Urea - - - 30" 10 

 Free lactic acid - 

 Lactate of ammonia - - - 

 Extractive matters (alcoholic and 



watery) - 



Lithic acid - I'OO 



Vesical mucus - 0'32 



Sulphate of potassa ... 3-71 



Sulphate of soda - - - - 3' 1 6 



Phosphate of soda ... 2'9-t 



Superphosphate of ammonia - - 1'65 



Chloride of sodium - - 4'45 



Chloride of ammonium - 1*50 



Phosphate of lime and magnesia - I'OO 



Silicic acid - ... Q'03 



Dr. Bence Jones has experimented very 

 carefully on the acidity of urine in health. His 

 results show that the amount of acidity is 

 always varying. Thus the urine passed longest 

 after food was generally the most acid, and 

 that voided while digestion was going on, 

 much less so, and in some cases even alkaline, 

 though the patient was in perfect health. 

 These conditions pertained, whether a pure 

 vegetable or animal diet was taken. In the 

 case of a pure vegetable diet, however, the 

 decrease in acidity, after taking food, was not 

 so marked as when a pure animal diet svas 

 observed ; the urine in the latter case some- 

 times becoming highly alkaline, but in the 

 former never exceeding neutrality. 



Other analyses of more recent date have 



4 at 4 



