300 ■ Transactions. 



Experiments that have been made by the present writer on pigeons 

 prove that birds are not immune to tutin. The minimum lethal dose by 

 mouth, however, was found to be high, and this probably accounts for the 

 apparent immunity, the ingestion of very large quantities of berries being 

 necessary to produce toxic symptoms. 



In the first experiment (Exp. 15) it unfortunately happened that the 

 pigeon used displayed a peculiar tolerance to the poison. This misled 

 to the belief that the minimum lethal dose was much higher than it really 

 is. The bird, weighing 314 grams, was subjected to successive doses, 

 equivalent to 2, 4, 6, 8, 10, 12, 16, 20 mlgm. per kilo of body-weight. The 

 solution of tutin was given by the mouth, and the experiment extended 

 over a period of ten days. The smaller doses had little effect. For a few 

 hours after each dose the bird was dull, apathetic, and disinclined to eat 

 or move about. It stood in a corner of the cage, with its feathers pufiecl 

 out, blinking heavily, and presented the appearance of a bird that had 

 overeaten itself, and was trying hard to go to sleep, but was too uncomfortable 

 to succeed completely. The last dose (20 mlgm. per kilo) was given on an 

 empty crop, and as no ill effect was anticipated — it being thought at this 

 time that in all probability birds really were immune — it was not closely 

 watched. But forty-five minutes later attention was attracted by the 

 flapping of its wings, and it was found lying on its back in convulsions. 

 One hour after the administration of the poison it was dead. Its weight 

 at death was 345 grams — a gain of 31 grams in ten days, which would seem 

 to indicate that tutin has no injurious influence on general metabolism. 

 That the bird actually received the doses stated is quite certain. The 

 sokition was very carefully measured in a hypodermic syringe having a 

 running-nut on the piston-rod, and dropped into the beak, which was held 

 open by the finger. There was no difficulty in the administration, and 

 every particle of the fluid was swallowed. 



As 20 mlgm. per kilo was obviously too great a dose, it was decided to 

 give to the next bird 1 mlgm. per kilo in excess of the largest ineffective 

 dose on the first bird. To this end a dose equivalent to 17 mlgm. per kilo 

 was administered by mouth to a fasting pigeon weighing 319 grams 

 (Exp. 16). In this case toxic symptoms — viz., twitching and tremulousness 

 of the head and wings, and attempts to vomit — made their appearance 

 within two minutes, violent convulsions appeared in four minutes, and 

 death occurred sixteen minutes after the administration. 



In contrasting these two experiments, it will be noticed that the " time 

 to kill " was greater in the first case by forty-four minutes, although the 

 dose exceeded the dose in the second case by 3 ml^m. per kilo. This 

 observation, taken in conjunction with the fact that symptoms did not 

 appear in the first case with a dose of 16 mlgm. per kilo, suggested the 

 possibility of the first pigeon having acquired some degree of immunity or 

 tolerance by the poison having been administered in gradually increasing 

 doses over a lengthened period. To test the validity of this supposition, 

 another pigeon was treated in the same way (Exp. 17). The experiment 

 extended over a period of three weeks, and a maximum of 10 mlgm. per 

 kilo was reached without the appearance of any marked symptoms, but 

 12 mlgm. per kilo proved fatal. 



The rapidity with which syihptoms ensued after a dose of 17 mlgm. 

 per kilo, and the speed with which a fatal termination was reached, pointed 

 to the dose being well above the lethal minimum. A dose equivalent to 

 15 mlgm. per kilo was therefore given by mouth to a pigeon weighing 



