1908. | Innervation in Vaso-motor Reflexes, ete. 359 
of the central end of the vagus, viz., fall of pressure and dilatation in the 
intestinal vessels. The dose was, as will be seen, not quite sufficient to 
completely convert the fall into a rise, but the intestinal dilatation is now 
replaced by constriction. In fig. 17, a similar tracing from the spleen, it is 
interesting to note that the preliminary short fall of pressure is accompanied 
by vaso-dilatation. | 
Although these tracings show that lessening of calibre in arterioles occurs, 
they do not exclude the possibility of this change being caused by inhibition 
of dilators, improbable as this may be. For this reason it was necessary to 
repeat the experiment on an organ in which the dilators can be excluded, 
such as the hind-leg, which can be deprived of dilators by section of the 
lumbar cord. Most of these experiments, however, were devoid of result, for 
a reason which was made clear by subsequent experiments. The animals, 
in fact, were eviscerated, in order to reduce the effect of the mere change in 
blood-pressure on the volume of the limb, and at that time I had not 
sufficiently realised the peculiarity of the vascular reflexes in the “dilator ” 
animal. Finding, as a rule, that it was impossible to obtain the typical 
reversal of the depressor effect by the usual dose of strychnine, I continued 
to inject more and more of the drug, only to put an end to all reflexes. 
The cause of this phenomenon is that dilator excitation, as I have shown, 
is an integral part of the depressor reflex, indeed, the main part in the 
“dilator” animal, and this component is not reversed in sign by strychnine, 
but merely ultimately reduced to zero. In the “ dilator ” animal, therefore, 
there will be a fall of pressure as long as any effect is obtained. It 
sometimes happens, however, by a lucky chance, that the dose of strych- 
nine falls just within the narrow limits between paralysis of the dilator 
excitation and that of the constrictor effect due to reversal of the normal 
inhibition. This is a somewhat important fact, since the normal constrictor 
effect of pressor reflexes is abolished by a small dose of strychnine, as will be 
seen later. The fact that the constrictor effect due to reversal of normal 
inhibition is the last to disappear shows that it is a different thing from the 
ordinary constriction ; but our present knowledge is insufficient to explain the 
difference. In the experiment of fig. 18 the spinal cord was transected in the 
lumbar region, in order to cut off the vaso-dilators; evisceration was 
performed and a large dose of strychnine injected. Notwithstanding the bad 
condition of the animal, excitation of the depressor produced a rise of 
arterial pressure, accompanied by diminution of volume of the limb, which was 
later overpowered by the rise of pressure. The result is quite definite, 
although small. 
It did not seem to me worth while to repeat the experiment, without 
