A Depressor Reaction. 



2 I 



In trying to separate these from the artery, we were confronted by 

 the peculiar difficulty that the reaction often disappeared suddenly 

 — a good reaction would be obtained by pulling a bit of tissue, 

 but on tying and dividing this, traction on either end would become 

 ineffectual. We have here apparently a very peculiar condition of 

 localized shock. This did not occur to the same extent in all ani- 

 mals, and furthermore, the reaction often reappeared after an hour. 

 In this way we were able to show that it is localized in the nerve 

 plexus rather than in the artery (we thought that the traction was 

 perhaps transmitted by the artery to some intracranial structure but 

 this is evidently not the case). When the carotid is pulled this 

 nerve plexus is stretched and thus stimulated. We are wholly 

 ignorant of the peripheral connection of these afferent fibers, of the 

 conditions under which they are stimulated in the intact body, and 

 of the functions which they subserve. As to the efferent path, our 

 evidence so far is mainly negative. 



As already stated, none of the cervical nerves are concerned, 

 and the splanchnics are also excluded. The fall occurs equally 

 well when the annulus of Vieussens and the inferior (middle) cer- 

 vical ganglion with all its branches are excised on both sides. It 

 therefore does not take the path of the ordinary accelerator or aug- 

 mentor fibers. It occurs even after the greater part of both stellate 

 ganglia are excised ; but then the effect is diminished. However, 

 we cannot yet state positively whether this diminution is due to the 

 elimination of a part of the afferent path, or merely to the general 

 shock attending the excision of these ganglia. We must conclude, 

 however, that the depressing impulse reaches the heart by none of 

 the known cardiac nerves. We do not know whether it acts by in- 

 hibiting some unknown augmentor nerves, or by stimulating some 

 unknown depressor nerves. We are actively engaged in further 

 investigation of this problem. 



Other points worthy of mention are the following : The max- 

 imum fall varies with different animals ; in some there is no fall, 

 or there may even be a rise, but, on the whole, fall is the rule, es- 

 pecially in vigorous animals. When traction is applied, there is 

 a latent period of several seconds, then a pretty abrupt fall, then 

 a slight recovery, and then the pressure runs at a constant low 

 level, so long as the traction is maintained or for at least ten min- 



