BODY TISSUES AND FLUIDS 435 



brought out from an examination of the normal concentration of the blood 

 and urine. Judging from their comparative composition, the kidney nor- 

 mally concentrates the creatinin 100 times, the urea 80 times, but the 

 uric acid only 20 times. Myers, Fine and Lough have pointed out that as 

 the permeability of the kidney is lowered in conditions of renal insuffi- 

 ciency, this becomes evident in the blood, first by a retention of uric acid, 

 later by that of urea, and lastly by that of creatinin, indicating that 

 creatinin is the most readily eliminated of these three nitrogenous waste 

 products, and uric acid the most difficultly eliminated, with urea standing 

 in an intermediate position. 



Urea. As indicated in the table above on non-protein nitrogenous con- 

 stituents the blood urea of a strictly normal individual taken in the morn- 

 ing before breakfast appears to fall within the comparatively narrow 

 limits of 12-15 mg. urea nitrogen per 100 c.c. of blood. Occasionally fig- 

 ures outside of the limits may be observed such as 10-18 mg., but figures 

 above 20 mg. can ordinarily be regarded as pathological. These state- 

 ments apply only to normal individuals on moderate protein diets where the 

 blood has been taken in the morning before breakfast. As Tileston and 

 Comfort, and Addis and Watanabe have shown, high protein diets may 

 considerably raise these figures, especially in certain individuals, while 

 Folin, Denis and Seymour have conclusively shown that lowering the 

 level of protein metabolism serves to reduce the non-protein and urea 

 nitrogen of the blood in mild cases of chronic interstitial nephritis. 



Since urea is the chief component of the non-protein nitrogen, and 

 since its estimation is considerably simpler than that of the non-protein 

 nitrogen, attention will be directed especially to the urea. Mosenthal 

 and Hiller have made a careful study of the relation of the urea to the 

 non-protein nitrogen in disease. They point out that the selective action 

 of the kidney maintains the urea nitrogen at a level of 50 per. cent or less 

 of the total non-protein nitrogen of the blood, but that an impairment of 

 renal function, even of very slight degree, may result in an increase of 

 the percentage of urea nitrogen. In advanced cases this may be even 

 higher than the 75 per cent given in the preceding table. 



To give a comparative idea of the values observed for urea nitrogen in 

 various pathological conditions, illustrative findings are given for a num- 

 ber of different conditions in the table below taken from a recent paper by 

 the writer, the data being from actual cases. As will be noted, the 

 conditions in which nitrogen retention may occur are quite numerous. 

 Marked urea retention may occur not only in the terminal stages of chronic 

 interstitial nephritis, but also in such conditions as bichlorid poisoning 

 and double polycystic kidney, and in some cases of acute nephritis. In 

 parenchymatous nephritis the findings are comparatively low. Kelatively 

 high figures are frequently noted in malignancy, pneumonia, intestinal 

 obstruction, lead poisoning, and sometimes in syphilis and cardiac condi- 



