396 



QUANTITY OF UREA. 



oz.] per day ; during hunger it sinks to 6'1 grms. [90 grains] per day. During 

 inanition, the maximum amount is excreted towards mid-day, and the minimum in 

 the morning. The daily amount of urea varies with the quantity of urine ; three 

 to five hours after a meal, the formation of urea is at a maximum, when it sinks 

 and reaches its minimum during the night. Muscular exercise, as a rule, does 

 not increase it (v. Voit, Fick and Wislicenus% 295), but only when deficiency of 



O, causing dyspnoea, occurs at the 

 same time (Oppenheim). 



Fig. 252. 

 1, 2, Prisms of pure urea; 3, rhomboidal plates ; 4, hexagonal tablets ; 5, 6, irregular scales 



and plates of urea nitrate. 



Pathological. In acute febrile inflammations, and in fevers generally ( 22, 3), the urea 

 increases until the crisis is reached, and afterwards it diminishes. After the fever has passed 

 off, the amount excreted is often under the normal. In some cases of high fever, although the 

 amount of urea formed is increased, it may not be excreted ; there is a retention of the urea, 

 which, later on, may lead to an increased excretion (Naanyn). In chronic diseases, the amount 

 depends largely upon the state of the nutrition, the metabolism, and also upon the degree of 

 fever present. Degenerative changes in the liver, e.g., due to poisoning with phosphorus, may 

 be accompanied by diminished excretion of urea and increased excretion of ammonia 

 (Stadehnann). It is increased in man by morphia, narcotin, narcein, papaverin, codein, 

 thebain (Fubini), arsenic (Gathgens), compounds of antimony, and small doses of phosphorus 

 (Bauer), which favour the decomposition of proteids, and by substances which increase the 

 bile formation in the liver (N. Paton). Quinine, which " spares " the proteids, diminishes it. 



Occurrence. Urea occurs in the blood (1 : 10,000), lymph, chyle (2 : 1000), liver, lymph- 

 glands, spleen, lungs, brain, eye, bile, saliva, amniotic fluid, and pathologically in sweat, e.g., 

 in cholera, in the vomit and sweat of uraemic patients, and in dropsical fluids. 



Formation. It is certain that it is the chief end-product of the metabolism of 

 the proteids. Less oxidised products are uric acid, guanin, xanthin, hypoxanthin, 

 alloxan, allantoin. Uric acid administered internally appears in the urine as urea ; 

 alloxan and hypoxanthin can be changed directly into urea. The urea excretion is 

 increased by the administration of leucin, glycin, aspartic acid, or ammonia salts 

 (Schulzen, Nencki). As yet it has not been definitely determined where urea is 

 formed, but the liver and, perhaps, the lymph glands, are organs where it is pro- 

 duced ( 178). 



In birds, the liver forms uric acid from ammonia. The liver can be readily excluded from 

 the circulation in birds, and Minkowski found that after this operation the uric acid was dimi- 

 nished and the ammoniacal salts were increased ( 178). 



Antecedents. During digestion, the proteids are converted into leucin, tyrosin, glycin, and 

 aspartic acid. If the amido-acids, glycin, leucin, or aspartic acid, or ammoniacal salts, be given 

 to an animal, the amount of urea excreted is increased. As the molecule of the amido-acids 

 contains only one atom of N, and the molecule of urea contains two of N, it is probable that 

 urea may be formed synthetically from these acids. It is possible that the amido-acids meet 



