Dehydration of the blood plasma and interstitial body fluids is the outstanding bodily change caused by severe diarrheal disease in infants. The initial therapeutic indication is usually an energetic attempt to repair this condition by the administration of fluids. It is obvious that a convenient and dependable method of determining the degree of dehydration and the effect of therapeutic measures would be useful clinically. Measurement of change in the water content of the blood plasma would seem to be the most practicable index of dehydration. The blood plasma should exhibit a wider range of change in water content than whole blood for the reason that the circumstances producing dehydration cause a much more extensive withdrawal of water from the plasma than from the red cells.
A number of rather time-consuming gravimetric procedures have been suggested for the purpose of ascertaining the degree of dehydration. Thus, the specific gravity of the