METABOLISM IN NEPHRITIS 335 



the blood. However, these materials are probably being held for further 

 use in the body and may be considered in a vastly different light from 

 those which are to be excreted. For the purposes of determining the 

 theoretical values of the non-protein nitrogen of the blood in cases in 

 which it was supposed that the nitrogen output should have equaled the 

 intake, the total quantity of retained nitrogen has been assumed to be 

 equally distributed in the body. From the figures given by Marshall and 

 Davis it is found that in an individual weighing 70 kilos the retention 

 of 30 grams of urea is equivalent to a rise of 40 mg. per 100 c.c. in the 

 urea of the blood. Applying the same principles to the total non-protein 

 nitrogenous products which are supposed to be excreted by the kidneys, 

 it is seen that for every gram of nitrogen retained, the non-protein nitro- 

 gen of the blood should be increased 1.33 mg. per 100 c.c. The same 

 figures could be applied, for similar reason, to increments in the urea nitro- 

 gen of the blood. 



How misleading a nitrogen balance study may be can be observed in 

 Table 17. This case of nephritis retained considerable nitrogen, 69 gm. 

 in 23 days, or 3 gm. a day; however, this is not due to faulty action 

 on the part of the kidney, but evidently is brought about because the tissues 

 are assimilating the nitrogenous material offered them. This is proved 

 by the fact that the non-protein nitrogen in the blood did not rise, but re- 

 mained at a constant level. 



As is shown in the section on renal function, it is not possible to 

 judge of the extent of kidney involvement according to its ability to ex- 

 crete nitrogen or any other substance. A slight injury of the kidneys may 

 produce an irritability ("hyposthenuria") and overactivity of these or- 

 gans and thus result in over- rather than undersecretion. Furthermore, 

 the level of the blood nitrogen or urea has to be taken into account. If 

 these substances are raised they furnish a greater stimulus to the kidney 

 and greater quantities will be excreted than if they are normal in amount. 

 This is made evident in the discussion on the cofficient of urea excre- 

 tion. Under these circumstances the curious condition may exist in 

 which the output of nitrogen equals the intake and yet the kidney's ability 

 to eliminate this substance may be markedly impaired as evinced by 

 the very high values for blood urea or total non-protein nitrogen. 



That different degrees of renal injury, even when due to the same toxic 

 substance, do not result in a constant effect upon kidney activity, may 

 be seen in Chart 2. Three dogs poisoned by uranium each showed a dif- 

 ferent state, as far as elimination of nitrogen was concerned. One ex- 

 creted this material in normal amounts, another in diminished quantities, 

 and in a third the elimination was distinctly greater than during the 

 control periods. Similar observations have been made many times in 

 nephritis. Hyposthenuria, protein destruction, polyuria, inspissation 



