344 Dr. W. M. Bayliss. On Reciprocal [Jan. 20, 
It appears to me that the only objection that can be brought against my 
interpretation of the experiment is that the increase of blood-flow may be 
in some way a consequence of the fall of general arterial pressure, the bulbar 
centres of gland-nerves may be excited by anzmia in a manner like that 
produced by the injection of extracts of duodenal mucous membrane,” or the 
rapid fall of pressure may induce a relaxation on the part of the arterioles 
themselves. Now, in the first place, the time at which the effect appears is 
not consistent with either of these suggestions. If the fall of pressure were 
the cause of the dilatation, this would be greatest during, or immediately 
after, the fall. On putting the question to the test of experiment, by the 
excitation of the peripheral end of the vagus nerve, I find that there is 
frequently a short period of increased rate of flow when the blood-pressure 
returns to normal. It was only seen when there was a rise of blood-pressure 
following the fall, and was absent after section of the chorda. It appears 
therefore, to be due to excitation of bulbar centres by anemia. In order 
to be able to detect any secretion of saliva, which would only be small, 
I performed a similar experiment on a dog, but could not observe any 
secretion. Apparently the secretory centres were not excited by the degree 
of anemia produced. It has been found difticult or impossible to excite 
reflexly electrical changes in glands. 
[Vote added May 25, 1908.—Professor Langley thinks that objection may be 
taken to the interpretation of vaso-dilation in the submaxillary gland in 
response to excitation of the central end of the vagus as representative of a 
general depressor reflex. The vagus nerve contains afferent fibres from 
various digestive organs, so that the effect on the salivary gland may well be 
a special reflex associated with the taking of food and different in its 
mechanism from genuine depressor reflexes. In order to meet this objection, 
I have repeated the experiment, but exciting the depressor nerve in the | 
rabbit. In this case also considerable increase of the rate of blood-flow 
through the gland deprived of constrictors was obtained on excitation. It 
seems, then, that the vagus effect in the cat may fairly be taken as a true 
depressor one. Moreover, as shown below, the reflex from the vagus in the 
cat consists, not only in the excitation of dilators, but also in inhibition of 
constrictors, so that, in any case, it shows the phenomenon of reciprocal 
innervation. 
Professor Asher informs me that he has obtained excitation of vaso-dilators 
to the submaxillary gland of the rabbit on exciting the depressor nerve. ] 
* Bayliss and Starling, ‘Journ. of Physiol.,’ vol. 28, p. 348, 1902. 
+ Bayliss and Bradford, ‘ Journ. of Physiol.,’ vol. 7, p. 224, 1886. 
