276 PROFESSOR C. R. MARSHALL ON 



By these methods 0"01 g. protoca techy 1-tropeine hydrochloride was found to 

 paralyse the terminations of the vagus in the heart for five minutes. At the end of 

 this period stimulation of the vagus generally produced a slight effect, and the effect 

 gradually increased with succeeding stimulations until the former normal condition 

 was reached, usually about twelve minutes after the injection. Occasionally the same 

 strength of stimulus failed to induce any action, and consequently it had to be slightly 

 increased. Thus, after the injection shown in fig. 2, stimulation with the secondary 

 coil at 20 cm. produced no effect up to eight minutes after the injection, whereas 

 stimulation with the coil at 16 cm. produced at this time a very good effect. I have 

 obtained the same result with other tropeines. 



When pilocarpine is used as a stimulus the paralysis of the vagal terminations does 

 not last so long. Thus the injection of O'Ol g. protocatechyl-tropeine hydrochloride, 

 after a previous injection of O'Ol g. pilocarpine, totally abolished the pilocarpine effect 

 for one and a half minutes only. The pilocarpine action then reappeared and in three 

 minutes had reached its previous form. The shorter period of paralysis in these 

 experiments as compared with that obtained when the vagus is stimulated electrically 

 is due to the fact that pilocarpine and protocatechyl-tropeine are to some extent 

 mutually antagonistic. 



Effect on Blood-Pressure. 



The commonest effect on the blood-pressure is a gradual fall, usually commencing 

 after the effect on the respiration has begun, and continuing when the respiration 

 spontaneously recovers, after this has become practically normal (cf. figs. 1 and 4). 

 The fall of blood-pressure continues for 1^ — 3 minutes, rarely more, and then the 

 pressure gradually returns to its previous height. It is not usually severe in extent 

 in rabbits; after a dose of 0*01 g. intravenously it generally amounts to about one- 

 third the normal blood-pressure. In cats the fall is often greater, and not infrequently 

 is preceded by a slight rise. The extent of the fall in the last-named animals is shown 

 in the following table, which expresses the result of two successive injections : — 



Minutes after injection ..... 3 9 



0004 g. Bp. in Mm. Hg 135 79 130 



0-002 g. Bp. in Mm. Hg 136 111 130 



Occasionally in cats a rise of blood-pressure has been the most prominent feature. 

 This effect is seen in fig. 3, which illustrates the greatest rise of blood-pressure I have 

 obtained with this substance. There was no fall below the normal subsequently. The 

 vagal terminations in the heart were found to be paralysed between A and B, and 

 to be again irritable between B and C. Two injections of O'Ol g. each were made in 

 the same animal later, and in both instances a rise of blood-pressure to nearly the height 

 of that shown occurred. The rise was more prolonged in each case, and the vagal 

 endings were paralysed for a longer time than after the injection illustrated. The 

 respiration was not graphically recorded in this experiment. 



