496 UKINB. [CHAP, xxxiv. 



URINK. 



Healthy urine is a clear, limpid fluid, of a pale straw colour, emitting a pecu- 

 liar and characteristic odour while warm, and exciting a saline and somewhat 

 bitter taste. As the solid constituents of this tiuid are entirely excrementi- 

 tious, and in great part derived from the disintegration of the tissues concerned 

 in the chemical changes connected with animal life, we should be led to expect, 

 that any alteration in the activity of these functions would lead to a correspond- 

 ing variation in the characters of the urine. Even in a state of health, the 

 qualities of the urine vary much ; and it has been found that active exercise 

 exerts a considerable influence upon the quantity of some of the most im- 

 portant constituents of this fluid. Nitrogenous matter, taken in greater 

 quantity than is required for the wants of the system, will be eliminated by 

 the kidneys in the form of urea, and the composition of the urine will there- 

 fore be influenced by the character, as well as by the quantity of the food.* 

 If an unusual quantity of water be taken into the stomach, a great proportion 

 will rapidly be eliminated by the kidneys, and the urine will be found to be 

 very dilute and of low specific gravity. Again, as the action of the kidneys 

 is materially affected by the activity with which the functions of the skin 

 are discharged, the condition of this great secreting surface has much to 

 do with the quantity and quality of the urinary secretion. Changes of tem- 

 perature, for the same reason, will cause the urine to vary in quantity. In 

 hot weather, when the functions of the skin are increased, and a large amount 

 of water is in this way removed from the system, in order to compensate for 

 the effects of the increased external heat, the urinary secretion is much dimi- 

 nished in quantity, and becomes more concentrated, while, in cold weather, 

 when this cooling effect of evaporation is not required, we find the amount of 

 urine much increased, and, therefore, diminished in density. A dry, or 

 humid state of the atmosphere, in consequence of affecting the rapidity of 

 cutaneous transpiration, will exert a certain amount of influence on the quan- 

 tity of water. It does not appear, however, that the quantity of the solid 

 constituents excreted in a given time is much altered by these circumstances. 

 The state of the nervous system will often be found to have a decided influ- 

 ence in modifying the characters of this secretion ; and various mental emo- 



* The frequency with which we meet with an excess of urea in the urine 

 of our countrymen is probably dependent in some measure upon the highly 

 nitrogenous nature of our food. On the continent of Europe this is so rare, 

 that some foreign observers appear hardly to credit the statements with refer- 

 ence to the frequent presence of excess of urea. 



