A Note on the Calculation of Water Exchange.

Newburgh and Johnston (1) have proposed a method for the determination of water balances that depends largely on the demonstrations by Benedict and Root (2) and others that, in the absence of sweating, losses of body weight not referable to the obvious differences between the weights of ingesta on the one hand and the urine and feces on the other hand, parallel closely the heat production of normal subjects and patients with diabetes and thyroid disease. The data of Benedict and Root (2) were secured under basal conditions. Newburgh and Johnston (1) have presented evidence, secured from a small number of selected normal subjects or subjects apparently normal in all respects except body weight, that the relation between heat production and insensible weight loss is maintained not only in the resting postabsorptive state, but also under conditions of feeding and activity, as long as the latter do not provoke sensible perspiration. Whether the same relation is maintained during abnormal states of hydration or during diseases involving particularly disturbances of the circulation, respiration or intermediary metabolism has not been ascertained with certainty and has been questioned by many observers; although Lashmet (3), from Newburgh's clinic, has proposed the application of the principle to the analysis of the water exchange in cases of nephritis with edema. It is not the purpose of the present paper to analyze the propriety of the assumptions made by Newburgh and Johnston nor the applicability of their techniques to the solution of problems of water exchange in patients with edema or dehydration. The immediate object is merely to call attention to certain unnecessary complications in their procedures for the calculation of the water exchange which seem to have escaped attention. The calculation procedures of Newburgh and Johnston (1), which they have set up in the form of balances, introduce no entirely new principles, but merely utilize certain well known chemical and metabolic relations. They can be briefly summarized in the following manner: