CHARACTERS OF NORMAL URINE. 395 



of physiological chemistry. In how far such a helief is confirmed 

 by fact, we leave the reader to determine from the following pages. 

 It is scarcely necessary to ohserve that the urine, when con- 

 sidered from a physiological point of view, must be regarded as a 

 fluid secreted by the organism from definite organs the kidneys 

 and containing certain soluble, nitrogenous, and saline sub- 

 stances, which have either become effete through the metamor- 

 phosis of animal matter, or have been conveyed into the animal 

 body, but are injurious to the animal functions. 



On examining normal human urine, we find that, when in a 

 fresh state, it is of a lighter or deeper amber colour, and has a 

 bitter, saline taste. When freshly passed, and while it retains 

 the temperature of the body, it is perfectly clear and transparent, 

 and has a peculiar, faintly aromatic odour. It is always somewhat 

 heavier than water, although its density never rises above T03 (in 

 the normal state). It distinctly reddens litmus paper, although 

 not always with equal intensity. When the urine is kept in a 

 clean vessel, it does not decompose so rapidly as has generally 

 been supposed, especially when it contains a considerable amount 

 of solid constituents. In urine, shortly after cooling, particularly if 

 it be concentrated, and after it has remained for a long time in the 

 bladder, as, for instance, in morning-urine, a light, cloudy film 

 becomes formed, which gradually sinks to the bottom. The acid 

 reaction gradually increases when the urine is kept for some time 

 at a mean temperature, and yellowish red crystals, which are even 

 discernible to the naked eye, are then deposited in the mucous 

 sediment, and on the sides of the vessel. In this condition the 

 urine may often continue unchanged for several weeks, without 

 undergoing further decomposition ; if, however, the urine be very 

 dilute, and the temperature rises above the mean, a different 

 process from that of acid fermentation is observed speedily to 

 occur. The urine is then found to be covered with a thin, fatty 

 shining, and frequently iridescent membrane, fragments of which 

 gradually sink to the bottom. The mucous sediment is then inter- 

 spersed with dirty yellowish white flakes, the urine acquires a pale 

 colour, its reaction becomes alkaline, and it begins to develop a 

 nauseous, ammoniacal odour. The reddish yellow crystals are 

 replaced by white granules, which are intermixed with colourless, 

 strongly refracting, prismatic crystals. 



The urine of carnivorous mammalia differs little from that of 

 man. It is perfectly clear, generally of a much lighter, almost 

 straw-coloured hue, and strongly reddens litmus paper, 

 urine of herbivorous animals, on the contrary, is usually turbid, 



