374 Dr. W. M. Bayliss. On Reciprocal [Jan. 20 
Constrictors and dilators indiscriminately are excited in all parts of the 
organism. But, since the skin is relatively more copiously supplied with 
dilators than the viscera are, it may happen that the net result is vaso- 
dilatation in the tormer and constriction in the latter. Moreover, since the 
volume of blood in the latter greatly exceeds that in the skin and neigh- 
bouring structures, the result on the general arterial pressure will be a rise, 
which itself will further increase the distension of the skin vessels. 
During the course of this research I have carefully looked out for any 
indications of a normal opposition between the visceral and cutaneous 
circulations. None has been met with. Any reflex involving constriction 
in the one area was found to have the same effect in the other, and similarly 
with the dilator reflexes. I refer to the point here since such a state of 
affairs is still occasionally spoken of as if it had some foundation in fact; it. 
would, obviously, if it existed, require treatment as a case of reciprocal 
innervation. It is scarcely necessary to repeat that an increase of volume 
in a limb, for example, in a pressor reflex, must not be taken as a proof of 
actual relaxation of arterioles; by preventing or diminishing the rise of 
general blood-pressure, it can be shown that their muscular walls are really 
in a state of contraction, which can be overcome by a sufficiently great internal 
- pressure. | 
VI. SUMMARY OF CONCLUSIONS. 
1. In depressor reflexes there is, along with inhibition of tone in the vaso-. 
constrictor centres, an excitation of vaso-dilator centres. This has been 
shown in the cases of the sub-maxillary gland, the penis, the hind-limb, the: 
ees ear, and probably the tongue. 
2. Correspondingly, in pressor reflexes, along with excitation of concen 
ee is,in appropriate conditions, inhibition of dilator tone. This is, however, 
more difficult to demonstrate. | 
3. Similarly, in the local, or Lovén, reflexes, there is also both excitation of 
dilators and inhibition of constrictors. 
4, The action of strychnine is to convert the inhibitory phase of all vascular. 
reflexes into an excitation, so that :— 
5. The depressor nerve produces a rise of blood-pressure under full doses of 
the alkaloid. It does this by exciting the constrictor centre by the same 
mechanism which normally inhibits it. 
6. In the “dilator” animal (see text) under strychnine, pressor reflexes 
become depressor, in that inhibition of dilators is converted into excitation. 
7. Various parts (synapses) of the reflex arc are differently sensitive to the: 
