

URINARY SYSTEM. 469 



tension increases, more urine, or, correctly speaking, more 

 water will be excreted ; so also when the arterial tension is 

 diminished, the urine will be less abundant. Physicians 

 know full well that there is no necessity for prescribing 

 diuretic medicines for. patients whose pulse is very soft and 

 feeble, and that in such cases the best diuretic will be a drug 

 that will stimulate the force of the heart and the circulation. 

 With this understanding the urinary secretion is very im- 

 portant, for it forms a sort of safety-valve by means of which 

 the blood is freed of an excess of water. After a meal there is a 

 sort of general plethora, an augmentation of the blood tension, 

 and consequently an abundant and diluted urine will flow 

 (iirina potus et cibi). In the morning, however, the urine 

 secreted during a previous night of repose is more concentrated 

 and scanty, because there has been no cause to increase the 

 quantity of liquid in the blood nor its pressure. The lungs 

 eliminate a slight amount of water. A proportion between 

 the weight of the organism and the quantity of solid residue 

 contained in the daily urine may be calculated. Each kilo- 

 gramme of the weight of the animal is represented by one 

 gramme of anhydrous urine. Yet this proportion may vary 

 according to the season or character of food. 



A man weighing 65 kilos, will excrete, on an average, 65 

 grms. of anhydrous urine. Nearly one-half (30 grms.) of the 

 anhydrous daily urine is represented by a substance, urea, 

 that we have mentioned before when speaking of all of the 

 other liquids of the organism. This substance is a nitrogen- 

 ous principle. More nitrogen is eliminated in urea than in 

 any other excrementitial product. It has been demonstrated 

 that the urea excreted is almost all (according to Lehmann, 

 four-fifths) that which can be produced from the food we eat ; 

 the remaining one-fifth may be accounted for when we recol- 

 lect that the respiratory excretion, as well as the epidermal 

 exfoliation and the secretion of sweat, contain a small amount 

 of urea. There is also found in the urea about one-fifth of 

 the carbon, which must be added to the 500 grms., that we 

 daily excrete by means of the lungs. 



The amount of urea may vary under the influence of cer- 

 tain well-defined conditions ; since it is the residue from the 

 combustion of albuminoids in the organism, its abundance 

 will depend upon the amount of animal food contained in 

 nutriment. 



In a general way it may be stated that there is a direct 



