128 IOWA ACADEMY OF SCIENCE 



of the vein should be expected and this is what we have found from 

 our experiments. 



The intravenous injection of epinephrin into the intact vein has not 

 as yet shown any rise in the venous* pressure as far as experimental 

 evidence goes. Prof. Henderson in the American Journal of Physiology 

 of November, 1910, reports that he has been unable to produce any 

 change in venous pressure by the use of epinephrin, while he has been 

 able to do so with the use of COo. 



There are, however, many factors which must be taken into consid- 

 eration before a final statement can be made. The fact that slight 

 changes of increased pressure are easily compensated for by the di- 

 lation of the very extensive and elastic venous structure ; in fact 

 that in venous circulation we have practically at one end, the cardiac, 

 an open channel and thus the easy escape of blood will prevent 

 any marked change in the venous pressure unless the contraction of 

 the vessels is maintained for some time, this epinephrin does not seem 

 to do as its action only lasts for a comparatively short time. The ar- 

 rangement of the muscle structure found in the veins is also of im- 

 portance in considering possible changes in blood pressure which can 

 be produced by the contraction of the venous wall. While we do find 

 in most veins some circular muscle fibres the extent of such fibres is 

 very small and they are much scattered over the vein. The arrange- 

 ment of muscle is mostly in a longitudinal direction and thus the 

 stimulation of the muscle while it may produce a slight contraction of 

 the circular fibres has most effect in shortening the vessel and in the 

 establishment of a more rigid wall rather than in the constriction of 

 the lumen and the elevation of blood pressure. 



Further experiments are needed before the true eft'ect of the in- 

 jection of epinephrin into the intact vein is determind. For while it 

 may cause the constriction of the excised vein this effect as far as 

 producing changes in blood pressure may be lost because of a greater 

 and more effective change in some other direction when the intact veins 

 are taken together as a whole. 



In conclusion we may say.- 



1. Experiments are here reported that show that epinephrin will 

 cause the constriction of the excised external jugular vein, similar to 

 its effect upon the arterial wall. 



2. That while intravenous injection may cause the constriction of 

 some veins the lack of circular muscle, in many veins prevents its uni- 

 form action throughout the venous system. 



