370 Dr. W. M. Bayliss. On Reciprocal [Jan. 20, 
In view of the special properties of the “dilator” animal, it is not. 
surprising to find that, in this condition, chloroform, if in not too high a. 
percentage in the air respired, sometimes causes a decided rise in arterial 
pressure, which may continue for several minutes. I can only suggest, in 
explanation, that in these cases the dilator centre was in tonic excitation 
before the administration of the drug, and that this excitation was either 
converted to inhibition or the centre paralysed by the latter, both of which 
would produce a rise by removing dilator impulses. 
On the whole it must be admitted that the effect of chloroform on the 
vaso-motor centres has not been so clearly made out as that of strychnine. 
The reason for this is its extremely depressant action on all vital activity, 
so that it is very difficult to so adjust the dose as to obtain the maximal 
reversal effect with the minimal paralytic effect. 
V. GENERAL REMARKS. 
It will, I think, facilitate the understanding of the results described in the 
previous pages if they are represented in the form of a diagram (fig. 27) on. 
the lines of that of Sherrington.* 
When this diagram is compared with that of Sherrington, it will be seen 
that I have used the name of “reciprocal innervation” in a somewhat 
extended sense, in that the state of affairs in the vascular reflexes is, in some 
respects, more complex than that in reflexes to voluntary muscles. The 
antagonistic impulses, instead of acting on separate muscles, must here be 
looked upon as affecting one and the same smooth muscle cell. There are 
also two distinct sets of afferent impulses, pressor and depressor, having 
opposite relations to the two centres, dilator and constrictor. | 
There is, indeed, as pointed out by Sherrington himself,+ another aspect: 
of reciprocal innervation as concerns the vascular system. The heart and 
the muscular coat of the blood-vessels may be regarded as antagonistic: 
muscles. The depressor nerve being the afferent nerve from the heart and 
aorta, will be expected to inhibit the antagonistic muscle, the wall of the: 
arterioles. I hope to investigate the reflexes from this point of view at an 
early date. 
In the present state of knowledge as to what is the essential meaning of 
excitation and inhibition in the central nervous system, it would be 
premature to attempt a complete explanation of the phenomena described in 
the preceding pages. At the same time I think it may be useful to indicate: 
* ‘Roy. Soc. Proc.,’ vol. 76, B, p. 286, 1905. 
t+ Loe. cit., p. 289. 
