1908. | Innervation in Vaso-motor Reflexes, ete. 351 
with the blood-pressure; perhaps these changes were rather less than would 
be expected from the amount of the rise of pressure obtained. 
The sub-maxillary gland, with sympathetic cut, drops being recorded as 
before, showed a distinct slowing of the rate of flow at the beginning of the 
excitation of the median, but this was rapidly overpowered by the rise 
of arterial pressure increasing the circulation. It appears that this organ is 
very sensitive to changes in the general blood-pressure. 
On the whole, it seems that, under experimental conditions, inhibition of 
dilator tone does not play a great part in pressor reflexes. No doubt, under 
more natural conditions, it has a greater importance. Moreover, from the 
theoretical point of view, it is of interest to be able to show that it does take 
place. 
Indirect evidence similar to that referred to above, with regard to the 
magnitude of the vascular reflexes in the “dilator” animal, applies here 
also. It is rather difficult to find in literature measurements of rise of 
arterial pressure on exciting central ends of sensory nerves ; but, on looking 
over several curves, I note that 70 mm. Hg is a high value. Bradford* 
states that the rise obtained from the central end of a dorsal root is of 
unusual magnitude; on measuring one of the curves he gives, I find that it 
amounts to 76 mm. Hg. To compare with this, in a “dilator” dog, on 
exciting the median nerve, there was a rise of 50 mm. Hg, viz., from 
130 mm. to 180 mm., and the rise would probably have been greater if the 
arterial pressure had been lower to begin with, as it appears to have been in 
Bradford’s experiments. It is difficult to avoid the conclusion that inhibi- 
tion of vaso-dilator tone plays some part in the rise of pressure in the 
“ dilator ” animal. | 
3. Lovén Reflexes. 
This type of reflex was first described by Loven in the ear of the rabbit 
and in the hind-leg of the same animal. It has subsequently been found in 
various other organs, so that it may fairly be regarded as of general occur- 
rence. Put briefly, when the afferent nerve from any particular organ is 
excited, there is produced, along with the usual pressor effect on the general 
blood-pressure, a vaso-dilatation in the organ itself. By this means the 
maximal supply of blood is sent to an active organ. I have previously 
shownt that dilator centres are excited, but, as yet, the proof is wanting 
that constrictor tone is inhibited. 
To decide this point, I made the following experiment: In a dog, the 
dorsal roots of the lumbo-sacral plexus on the left side were divided, and the 
* ‘Journ. of Physiol.,’ vol. 10, p. 400, 1889. 
+ ‘Journ. of Physiol.,’ vol. 28, p. 292, 1902. 
