METABOLISM IN NEPHRITIS 357 



numerous substances (urea, salt, water, phthalein) and may therefore be 

 accepted as an empirical truth. It may arouse speculations as to the role 

 the glomeruli and tubules play in this connection. This unsolved side of 

 the problem, however, need in no way impair the clinical importance of 

 the observation. From the clinical point of view the use of lactose and 

 potassium iodid to determine renal function has been found to be imprac- 

 ticable not only because the methods are difficult to carry out, but also 

 because the significance of the tests is not clear (Rowntree and Fitz, Vol- 

 hard, Siebeck(fr), Monakow(a) and others). 



Technic of the Lactose and Potassium Iodid Tests. Lactose. About 

 TO c.c. of a 10 per cent solution is put into an Erlenmeyer flask ; a fresh 

 flask is used for each test; the lactose solution is pasteurized on three 

 successive days at 75 to 80 C. for four hours (heating to 100 C. gives 

 the lactose a brown color and makes subsequent readings in the polariscope 

 difficult or impossible). Unless the directions are carefully followed un- 

 toward reactions, such as a chill, may follow; 20 c.c. of this solution (i e. 

 2 grams of lactose) are injected intravenously; the urine is examined 

 every hour or one-half hour subsequently by means of Nylander's reaction 

 to determine the absence or presence of lactos.e, and quantitatively by the 

 polariscope; a normal individual will eliminate about 90 per cent of the 

 lactose in less than four or five hours ; if glomerular function is impaired 

 the lactose excretion is prolonged and a smaller amount of lactose may be 

 recovered (Schlayer and Takayasu). 



Potassium Iodid. 0.5 gm. of the drug is given by mouth ; the urine is 

 examined every two hours by Sandow's method; the average duration in 

 normal persons necessary for excretion is 44 hours though no observa- 

 tion under 60 hours should be considered as indicating a delayed elimina- 

 tion (Schlayer and Takayasu). The dose of potassium iodid does not 

 appear to have much bearing on the test, though it must be recognized that 

 the various tests for the identification of potassium iodid in the urine vary 

 much in their delicacy and that there is a large personal equation in judg- 

 ing of the absence or presence of slight amounts of iodid by means of any 

 of these reactions. These factors may account, for the wide variations in 

 the normal elimination time for potassium iodid as described by different 

 authors, the limits being 25 to 48 hours according to Rowntree and Fitz. 



The Constituents of the Blood. 



For the significance of sugar, cholesterol, calcium, phosphates, sodium 

 chlorid, proteins and non-protein nitrogenous constituents of the blood 

 reference is made to previous chapters in the section on nephritis. 



The Coefficient of Urea Excretion 



By means of a mathematical formula, which made use of the concen- 

 tration of urea in the blood and urine, Ambard expressed the power of 



