THE ACTIONS OF PHYSOSTIGMA AND ATROPIA. 581 



In order to define the limits of the counteracting influence of atropia upon 

 the lethal action of physostigma, three series of experiments were made. 



The chief objects of the two first of these were to ascertain the maximum 

 dose of physostigma that can be successfully antagonised by atropia, and the 

 range of doses of atropia that can successfully antagonise lethal doses of 

 physostigma. In each series, a constant interval of time was maintained 

 between the administration of the two substances ; but in the first, atropia was 

 administered five minutes before physostigma, while in the second, physostigma 

 was administered five minutes before atropia. These intervals of time were 

 selected in preference to simultaneous administration because, practically, it is 

 impossible for one experimenter to inject the two substances into different 

 regions exactly at the same moment, and further, because it seemed probable 

 that a difference would be found to exist in the counteracting power of atropia 

 according as it is given before or after physostigma. In both of these series, 

 experiments were made, in the first place, with the minimum-lethal dose of 

 physostigma, and in combination with it, various doses of atropia were 

 administered, ranging from one that was too small to prevent the lethal action, 

 through a number that were able to prevent death, until a dose was found 

 whose administration resulted in death. Similar experiments were made with 

 a dose of physostigma one and a half times as large as the minimum-lethal, 

 then with one twice as large as the minimum-lethal, and so on, at the same rate 

 of progression, until a dose of physostigma was reached that was too large to 

 be successfully antagonised by any dose of atropia. 



The chief object of the third series of experiments was to ascertain within 

 what limits of time between the administration of the two substances successful 

 antagonism occurs. In the experiments of this series, a constant dose of physo- 

 stigma was given along with various doses of atropia, and with each dose of 

 atropia several experiments were made which differed from each other by a 

 difference in the interval of time between the administration of the two 

 substances. On this plan two sets of experiments were performed, in one of 

 which atropia was given before physostigma, and in the other of which it was 

 given after ; and subsequently these two sets of experiments were connected 

 together by a third, in which atropia, in various doses, was administered nearly 

 simultaneously with the same dose of physostigma as was given in the two 

 other sets of experiments. 



All the experiments of this portion of the research were performed on 

 rabbits. In the great majority of the experiments, the weight of the animal 

 was about three pounds, but when it was below or in excess of this, the doses 

 of the substances administered were calculated for three pounds weight of 

 animal. 



In the description that will now be given of these experiments, the doses 



VOL. XXVI. PART III. 7 M 



