Physical Characters of Urine. —The characters of the urine excreted by the healthy kidney are well defined ; and they undergo , marked alterations in disease. It will, there be of value to state here the characters and chemical constitution of healthy urine and the chief alterations urine undergoes in disease. This will be of great value in understanding the results of the diseased conditions of the kidney described in the section which follows.
Urine when freshly passed is of an amber colour, clear and transparent, and with a peculiar aromatic odour, and of slightly acid reaction.
Its specific gravity is usually about 1020.
The quantity passed in 24 hours by a healthy adult man is between 50 and 60 fluid ounces. It varies not only according to the quantity of water taken in by the mouth, but according to the external temperature and the amount of exercise. The kidneys and skin co-operate to this extent, that if much water is removed by the skin as sweat, as in warm weather and after exercise, less is expelled by the kidneys. In cold weather the skin is less active, and a greater quantity of water will be produced by the kidneys.
Nervous influences also affect the quantity. Thus after hysterical attacks a large quantity of clear urine is often passed. In many persons also excitement of any sort is attended by a very rapid secretion of urine, producing great discomfort if they are in circumstances hinder ing the emptying of the bladder. This should be remembered in the case of children to whom the pleasure of some entertainment is frequently lessened by a similar circumstance.
Chemical Constitution of Urine is shown in the following table :— Gases, principally carbonic acid gas, nitrogen and oxygen being in very small quantity, are also contained in urine to the amount of nearly 16 per cent.
The solid constituents consist of two classes of substances : (1) inorganic salts, namely, com mon salt (chloride of sodium), sulphates, and phosphates, and (2) organic bodies, bodies con taining nitrogen, namely, urea, uric acid, hip puric acid, kreatinin, &c. It is instructive to observe the sources of these substances. Chlo rides occur in all the fluids of the body ; sul phates arise from the decomposition of albu minous bodies; and phosphates have as their source albuminous bodies, the phosphates exist ing in bone, and phosphorus present in nervous structures. An excess or diminution in the quantity of any of these substances cast out of the body may thus aid in the recognition of a disease. Thus the quantity of phosphates in the urine is increased in diseases of nerve centres and of bone.
The chief constituents, however, are the nitrogenous, area and uric acid, the former specially, of which a large amount is excreted, as indicated in the table.
Urea contains the four elements, nitrogen, hydrogen, oxygen, and carbon, nitrogen form ing half its weight. While, therefore, the lungs expel from the body carbonic acid in particular, the kidneys expel nitrogen. Both of these sub stances show decompositions going on in the body, the carbonic acid being the result of the breaking down of starch, sugars, fats, and al bumin also, while urea and uric acid are the products of the decompositions of nitrogenous bodies only, of which albumin is the type.