BODY TISSUES AND FLUIDS 441 



of the three nitrogenous waste products, uric acid, urea, and creatinin 

 (see staircase table on page 439). 



In various studies on nitrogen retention by Myers and associates it 

 was soon noted that the creatinin of the blood was appreciably increased 

 only after considerable retention of urea had already taken place and the 

 nephritis was rather far advanced. It was further observed that those 

 cases in which the creatinin had risen above 5 mg. per 100 c.c. of blood 

 rarely showed any marked improvement, and almost invariably died within 

 a comparatively limited time. The only exceptions were cases where the 

 retention was due to some acute renal condition. In a recent paper Myers 

 and Killian (6) have discussed in detail the observations on a series of 100 

 nephritics with high creatinin findings, while more recently Myers has 

 again reviewed the general subject. It may be stated that, of 85 cases 

 having over 5 mg. of creatinin, all the cases, with three exceptions, are 

 known to be dead. Most of these cases lived from 1 week to 3 months al- 

 though there were three cases that lived 1, 2 and 3 years respectively. 

 Of the three exceptions two were acute cases that recovered, while one 

 was followed for only a short period. Among the cases having very high 

 blood creatinins there were many who were able to be up and about and 

 some who showed considerable clinical improvement. In these cases the 

 blood creatinin gave a particularly good insight into the true nature of the 

 condition. 



The amount of the increase of the creatinin of the blood should 

 be a safer index of the decrease in the permeability of the kid- 

 ney than the urea, for the reason that creatinin on a meat free diet 

 is entirely endogenous in origin and its formation (and elimina- 

 tion normally) very constant. Urea, on the other hand, is largely 

 exogenous under normal conditions and its formation consequently 

 subject to greater fluctuation. For this reason it must be evident that 

 a lowered nitrogen intake may reduce the work of the kidney in eliminat- 

 ing urea, but cannot affect the creatinin to any extent. Apparently the 

 kidney is never able to overcome the handicap of a high creatinin accumu- 

 lation. It would seem that creatinin, being almost exclusively of endog- 

 enous origin, furnishes a most satisfactory criterion as to the deficiency 

 in the excretory power of the kidneys and a most reliable means of follow- 

 ing the terminal course of the disease, though it should be noted that 

 urea, being largely of exogenous origin, is more readily influenced by 

 dietary changes, and therefore constitutes a more sensitive index of the 

 response to treatment. 



Creatin. The methods of estimating the blood creatin are considerably 

 less satisfactory than those for creatinin. Figures obtained with the 

 original Folin method were apparently too high. Kecent methods and 

 observations of Denis (6) and Folin and Wu give the normal creatin con- 

 tent of blood as from 3 to 7 mg., with an average of about 5 mg. The 



