"302 EXPhPJMEXTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



If it increase the excitability of both roots and ends, immediate 

 slowness should occur, whether it be injected into the jugular 

 ■or carotid, and this should become more marked after 15 or 

 20 seconds. If, like physostigma, it increase not only the 

 •excitability of the vagus-ends, but that of the quickening centre 

 in the head, injection into the jugular should be followed by 

 immediate slowing, which would become less marked when the 

 <lrug reached the head, and injection into the carotid by an 

 immediate quickening, which would become less or give place 

 to slowness when the drug reached the heart. 



At first sight one might think that, after time had been 

 allowed for the drug to pass round the circulation and be applied 

 both to the vagus-roots and ends, its action on the heart would be 

 the same whether it had been originally injected into the jugular 

 or into the carotid ; but this is not the case, for that organ 

 towards which the drug was injected gets a larger dose, and its 

 action is more strongly excited than that of the other. Thus 

 when physostigma is injected into the carotid, the quickening 

 •centres are stimulated and the pulse-rate rises ; and, although 

 the pulse falls somewhat after the vagus-ends have also been 

 acted on, it nevertheless continues above the normal, the stimu- 

 lation of the vagus-ends not being able to counteract the still 

 more excited quickening centres. When it is injected into the 

 jugular, the vagus-ends get the largest dose ; and although the 

 pulse, which is at first made very slow, may afterwards become 

 quicker when the drug reaches the brain, it nevertheless does 

 not reach, the normal rate, the quickening centres being unable 

 to counteract the more strongly excited vagus. If the vagus be 

 then cut, however, the pulse becomes quicker than it would 

 have done had no physostigma been given ; or, if the vagi be 

 first cut and the drug injected, the pulse is quickened at 

 once. One might think that, since the drug acts on the vagus- 

 ■ends, its action should remain after the nerves themselves 

 have been divided; but since it is by increasing the excita- 

 bility of the ends that it acts, if we separate these ends 

 from the roots, and thus remove their normal stimulus, their 

 increased excitability can have but little effect. In order 

 to measure the amount of increase in the excitability of 



