448 THE URINE. 



sensation at and near the orifice of the urethra. Then, the 

 effort of the will being directed primarily to the muscles of 

 the abdomen, and through them (by reason of its tendency 

 to act with them) to the urinary bladder, the latter, 

 though its muscular walls are really composed of invo- 

 luntary muscle, contracts, and expels the urine. (See also 

 p. 223.) 



The Urine : its general Properties. 



Healthy urine is a clear limpid fluid, of a pale yellow or 

 amber colour, with a peculiar faint aromatic odour, which 

 becomes pungent and ammoniacal when decomposition 

 takes place. The urine, though usually clear and trans- 

 parent at first, often becomes as it cools opaque and 

 turbid from the deposition of part of its constituents pre- 

 viously held in solution ; and this may be consistent with 

 health, though it is only in disease that, in the tempera- 

 ture of 98 or 1 00, at which it is voided, the urine is 

 turbid even when first expelled. Although ordinarily of 

 pale amber colour, yet, consistently with health, the urine 

 may be nearly colourless, or of a brownish or deep orange 

 tint, and, between these extremes, it may present every 

 shade of colour. 



When secreted, and most commonly when first voided, 

 the urine has a distinctly acid reaction in man and all car- 

 nivorous animals, and it thus remains till it is neutralized 

 or made alkaline by the ammonia developed in it by 

 decomposition. In most herbivorous animals, on the con- 

 trary, the urine is alkaline and turbid. The difference 

 depends, not on any peculiarity in the mode of secretion, 

 but on the differences in the food on which the two classes 

 subsist : for when carnivorous animals, such as dogs, are 

 restricted to a vegetable diet, their urine becomes pale, 

 turbid, and alkaline, like that of an herbivorous animal, 

 but resumes its former acidity on the return to an animal 

 diet ; while the urine voided by herbivorous animals, e.g., 

 rabbits, fed for some time exclusively upon animal sub- 



