FORMATION OF UREA 2O3 



of it is removed from the body by the kidneys, and double 

 nephrectomy means death from its retention. Its formation 

 is constant and its removal necessary. Its presence in the 

 blood seems to be the normal stimulus exciting the activity 

 of the cells of the convoluted tubes. 



Whether urea is produced directly in the tissues, or 

 whether only certain substances antecedent to it are there 

 formed, it cannot be doubted that it is the chief final pro- 

 duct of nitrogenous ingesta and nitrogenous dissimilation. 

 It is practically the only way in which the nitrogen of pro- 

 teid foods can escape from the body. It exists not only in 

 the blood but in the lymph, vitreous humor, sweat, milk, sa- 

 liva, etc. It has been stated that the taking of large quanti- 

 ties of liquids lowers the specific gravity of the urine by di- 

 luting it ; this is true, but the actual amount of urea is in- 

 creased somewhat by such a procedure. It is not surprising 

 that the quantity of urea is largely increased when much 

 nitrogenous food is taken, and that it is greatly decreased 

 by an exclusively vegetable diet. Anything, like exercise, 

 which will increase actual tissue metabolism, will increase 

 the output of urea, while anything retarding tissue metabol- 

 ism, like alcohol, will decrease the output. The average 

 amount of urea for 24 hours is 350 to 450 grains. 



Formation of Urea. Seeing that urea is the typical end 

 product of the physiological oxidation of the proteids, it be- 

 comes of interest to determine, if possible, where urea for- 

 mation takes place. It is known that the liver is very active 

 in producing this substance ; but it is not alone by this organ 

 that urea is formed. At the present time the prevailing 

 opinion is that, for the most part, the proteids under destruc- 

 tive metabolism in the tissues do not reach the urea stage of 

 transformation, but are converted into ammonia compounds 

 (which differ very slightly from the urea in chemical compo- 

 sition), and these compounds are conveyed by the blood to 

 the liver, where the slight change necessary to make them 

 urea is effected under the influence of this organ. Ammon- 



