312 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



to reach a frog's heart, its beats become slower and slower, and 

 at last cease altogether, the ventricles remaining widely dis- 

 tended, just as they would do if the vagus were strongly 

 galvanised. If nicotia be then injected into the frog or mixed 

 with the serum supplying an excised heart, no alteration is 

 observed ; and if nicotia be injected before the rauscaria, the 

 latter poison stops the heart just as usual, although the nicotia 

 may have so paralysed the vagus that no irritation whatever 

 applied to its trunk could act on the heart. But, if atropia be 

 used instead of nicotia, the effect of the muscaria is at once 

 destroyed, and the heart, which was standing quite still, imme- 

 diately begins to beat. If the atropia be applied first, and 

 muscaria given afterwards, it has no effect. Hence we see that 

 nicotia has paralysed some part of the inhibitory apparatus 

 farther away from the motor ganglia than that on which mus- 

 caria acts, while atropia has acted either on the same part as 

 muscaria, or on some otlier one which lies between it and the 

 motor ganglia. 



Now, as the inhibitory effect produced by muscaria. is not 

 developed all at once, but goes on slowly increasing till it makes 

 the heart stand still in diastole, it seems probable that its 

 stimulating action is exerted on a ganglion, rather than on a 

 nerve-fibre, and we therefore suppose that it acts on the inhibi- 

 tory ganglion i. As the action of nicotia is exerted on some- 

 thing farther from the heart than I, our first idea is that it 

 must be the nerve-fibres V. But on applying nicotia to the 

 trunk of the vagus, after fixing the heart in Coats' apparatus, 

 we find, on irritating the nerve above the point, that it still 

 conducts impressions and causes stoppage of the heart. We are 

 thus led to suppose the existence of an intermediate apparatus 

 on which nicotia acts ; but, whether or not this intermediate 

 part simply consists of nerve-fibres less protected from the 

 poison than those in the trunk, we cannot say. As atropia 

 destroys the action of muscaria, it may act like muscaria on i ; 

 but the fact that muscaria does not destroy that of atropia 

 would lead me to refer the action of the latter to a part betvveen 

 I and M, which is represented by B. Of what nature this part 

 is we know nothing; but that such a part exists is rendered 



