THE URINE. 375 



less severe according to their special character and the rapidity of their 

 production. This poisonous influence is especially manifested in its 

 action upon the nervous system, causing an abnormal irritability, de- 

 rangement of the special senses, delirium, insensibility, coma, and death. 

 These effects are more particularly marked in the case of urea after 

 suppression of the urine ; a complete stoppage of the elimination of this 

 substance in the human subject usually producing a fatal result in three 

 or four days. 



The excrementitious matters, however, are not to be considered as 

 poisonous, or even deleterious, in the quantities in which they normally 

 occur in the animal solids and fluids. On the contrary, they are the 

 natural products of the functional activity of the animal system, and 

 are, therefore, as essential to the continued manifestation of life as the 

 nutritious materials supplied by the food. It is only when the regular 

 course of their elimination is retarded that they interfere with the due 

 performance of the functions, by deranging the natural constitution of 

 the tissues. 



A variety of excrementitious substances are produced in the body, 

 some of which are probably eliminated, in small proportion, with the 

 perspiration or with the feces. The carbonic acid, exhaled in large 

 quantity from the lungs, is to be regarded as belonging to this class, 

 since it is produced in the substance of the tissues and constantly 

 discharged by respiration. But the most important substances, 

 usually included under the head of excrementitious matters, are distin- 

 guished by the fact that they contain nitrogen as one of their ultimate 

 elements, and that they otherwise exhibit a remarkable analogy with 

 each other in their chemical composition. They accordingly form a 

 natural group of organic substances, resembling each other in their 

 origin, their constitution, and their physiological destination. They are 

 furthermore associated together by the circumstance that they are all 

 eliminated from the body by the urine, of which they form the essential 

 and characteristic ingredients. 



The urine is therefore the only animal fluid which is solely an excre- 

 tion. It is a solution of the nitrogenous excrementitious matters of the 

 animal frame ; and by its abundance and composition it indicates the 

 activity of the healthy metamorphosis of the organic tissues and fluids. 

 Beside its nitrogenous ingredients, it contains also most of the mineral 

 salts which are discharged from the body ; and by the water which holds 

 these solid matters in solution it forms the channel for a large propor- 

 tion of the fluids passing daily through the system. Furthermore, acci- 

 dental or abnormal ingredients, introduced into the blood, almost 

 invariably find their way out of the system by the kidneys, and thus 

 appear as temporary ingredients of the urine. The constitution and 

 physiological variations of this fluid during health, and its alteration 

 in disease, are regulated by the corresponding changes of nutrition or 

 activity in the body at large. The urine is therefore one of the most 

 essential products of the animal system, and its formation is second 

 in importance only to the function of respiration. 



