THE ADRENAL GLANDS 739 



pressure produced by the injection is then a very fair measure of the 

 amount of epinephrine contained in it. It has been shown that the re- 

 sults obtained by the chemical method agree very closely with those obtained 

 by the physiological, but it should be remarked that it is difficult to see how 

 the physiological method could 'be accurate in all cases, since it has been 

 shown that with great dilution of epinephrine a reversed effect a vaso- 

 dilatation may be obtained. Attempts to assay the strength of an 

 epinephrine solution by investigating the effects which it produces on 

 other preparations, such as isolated loops of intestine or uterus, or the 

 enucleated eyeball of the frog, are not always successful, since the effects 

 are not alone dependent on the concentration of epinephrine in the 

 extract. When such preparations are used for quantitative purposes, 

 .the strength of the extract may be judged by finding the extent to which 

 it can be diluted and still remain active. 



Quite apart from the foregoing possible sources of error, it must be 

 remembered that the results merely give us an idea of how much epineph- 

 rine may have been contained in the gland at the time of its excision. 

 They can not tell us how much epinephrine the gland was secreting. Prior 

 to excision as much of this hormone might have been undergoing a process 

 of manufacture in the gland as was being discharged from it, so that the 

 assayed amount would represent merely the balance of production and loss 

 of hormone by the gland. We might quite well find that the amount of 

 epinephrine in the excised gland was normal under conditions where 

 there had been an excessive discharge of it into the blood; that is to say, 

 loss and production might have been equal. Where, however, a marked 

 deficiency is found to exist, it probably indicates that exhaustion of the 

 power of producing epinephrine was taking place. 



The Epinephrine Content of the Blood. The second method, in which 

 blood from one animal is tested for its epinephrine effect by intravenous 

 injection into another animal or by applying it to some isolated prepara- 

 tion on which epinephrine acts, has yielded important results. Since 

 serum contains all the epinephrine of blood, it can be conveniently used 

 for the tests (Stewart and Rogoff). The isolated physiological prepara- 

 tions that have been used in testing for epinephrine in the animal fluids 

 are as follows: 



1. A segment of the small intestine of a rabbit, suspended in oxygen- 

 ated Locke's solution at body temperature. 



2. A segment of the uterus of a nonpregnant rabbit similarly prepared. 



The apparatus used for observing the contractions of either prepara- 

 tion consists of a small glass chamber furnished below with a hook to 

 which one end of the segment is attached, the other end being connected 



