In a previous publication,1 facts were presented showing that an adequate circulation was necessary for the production of wheals in the human skin, and certain clinical conditions were discussed in which lessened or absent wheal formation following the intracutaneous injection of a codeine solution was attributed to decreased circulation in the skin. In this group were a limited number of patients who were acutely dehydrated, but the data were insufficient to decide whether actual decrease in blood volume, because of the dehydration, was the fundamental factor in the lessened circulation on which decreased wheal formation depended. It seemed worth while, therefore, to continue these observations to learn whether dehydration itself, independent of other factors, such as low blood pressure, would decrease the peripheral blood flow sufficiently to lessen wheal formation. The reaction to the intracutaneous injection of codeine was taken as a representative of the class of substances that