20 



Scientific Proceedings (25). 



10 (266) 



A depressor reaction obtainable by traction on the 

 carotid artery. 



By TORALD SOLLMANN and E. D. BROWN. 



[From the Pharmacological Laboratory of Western Reserve Univer- 

 sity, Cleveland, Ohio.~] 



By pulling on the carotid artery, a very marked fall of blood- 

 pressure (often of 50 to 90 mm. Hg) and increase of respiration 

 can be produced. Our attention was directed mainly to the fall 

 of pressure, but most of the remarks below apply also to the 

 respiratory phenomenon. If the carotid is divided, the phenomena 

 can only be elicited by traction of the cephalic, but not of the car- 

 diac end. It is therefore not due to kinkage of the aorta. It 

 occurs after both carotids are tied, so that it is not due to cere- 

 bral anemia. It does not occur on traction of either end of the 

 cervical vagus, depressor, or sympathetic, so that it is not produced 

 by accidental stimulation of these nerves. It does occur after all 

 of these nerves are divided on both sides (in dogs, cats and rabbits) 

 so that these nerves are not concerned in the phenomena. 



The following remarks apply to dogs in which both vagi were 

 divided. Oncometric observations show that the volume of the 

 abdominal organs decreases with the fall of blood-pressure, so that 

 this fall cannot be vascular. In further support of this conclusion, 

 it was found that the fall occurs after section of both splanchnics, 

 and after clamping the aorta at the diaphragm. The fall must 

 therefore be cardiac. The heart rate is commonly somewhat 

 slowed, but this is neither constant nor pronounced. Myocardio- 

 graphic tracings show that the fall of pressure is indeed due to 

 weakening of the cardiac contractions. We have tried to trace 

 out the path which is taken by this highly peculiar and novel 

 reflex. By following the carotid upward, we found that the reac- 

 tion could be obtained from the region of the common carotid 

 containing the origin of the internal carotid, but from none of the 

 other branches, or at least only to a very slight extent. It could 

 also be elicited by electric stimulation of this region. The internal 

 carotid at this point is surrounded by a rich plexus of nerve fibers. 



