88 MEDULLA 



that an increase in the concentration of epinephrine in the blood 

 leaving the adrenals was in itself evidence of an increased rate 

 of secretion. Since many physiological conditions are accom- 

 panied ,by a decrease in the rate of blood flow through various 

 organs, 243 neglect to consider this factor will invalidate the 

 conclusions based solely on concentration changes in the blood. 

 In the following sections we shall consider the various pro- 

 cedures used in the biological assay of the epinephrine content 

 of the blood and the methods used for determining the output 

 of epinephrine from the adrenals. Besides the biological 

 methods of assay listed below, certain of the more sensitive 

 chemical methods already described have also been utilized in 

 studies on the physiology of the medulla. Instead of deter- 

 mining the rate of secretion by analysis of the blood, attempts 

 have been made to obtain this data by analysis of the epi- 

 nephrine content of the adrenals in various conditions. Deple- 

 tion of the epinephrine store indicates a stimulation of the rate 

 of secretion. However, if the rate of synthesis follows changes 

 in the rate of secretion, such depletion will obviously not occur. 



METHODS FOR THE BIOLOGICAL ASSAY OF EPINEPHRINE 



1. The intestinal strip method. The inhibition of intestinal 

 muscle by epinephrine serves as a very delicate test for epi- 

 nephrine. Cannon and Hoskins 105 claim this test to be sensitive 

 to epinephrine in a dilution of 1 to 400 millions; Stewart and 

 Rogoff 588 claim 1 to 800 millions. The blood to be tested is 

 added to Ringer's solution in which is suspended a strip of 

 intestine (rabbit or guinea pig) arranged to record on a kymo- 

 graph. The resulting inhibition is compared with that ob- 

 served after the addition of a known quantity of epinephrine. 



Although extremely sensitive, this method suffers from the 

 defect that interfering substances present in the blood may 

 also inhibit intestinal movements. 587 



2. Blood pressure method. This method was first suggested 

 by Houghton and carefully worked out by Elliott. 177 Al- 



