were mostly when the thallium v/as compounded as an acetate or a, nitrate, both of 

 which forms are more readily soluble than the sulphate. The present investiga- 

 tions have to do only with thallium as a sulphate, as it is in that form that it 

 is used in rodent control. The indications, therefore, are that 25 milligrams per 

 kilogram is generally a lethal dose for mammals, large or small. 



Lethal Dose for Birds 



I 



\ 



In the case of ducks, ravens, pigeons, and doves, the minimum lethal dose 

 administered orally is greater and more variable, ranging from 50 to 100 milligrams 

 per kilogram. A duck weighing 750 gram.s (the average weight) requires 37.5 milli- 

 grams of thallium sulphate for a lethal dose (being 50 milligrams per kilogram) . 



Possibility of Secondary Poisoning in Man 



In accordance with the assumption that in man 25 milligrams per kilogram is 

 the lethal dose, a man v.^eighing 68.2 kilograms (150 pounds) would require in sec- 

 ondary poisoning 1,705 milligrams of thallium sulphate for a fatal dose. To get 

 such a dose from eating ducks that had died from thallium poisoning, he would have 

 to eat at one meal at least 45 entire ducks weighing 750 gram.s each (including the 

 viscera) . The fact however, that the viscera retain about one-third of the poi- 

 son, which thus would not be eaten, increases to 67.5 the number of eviscerated 

 ducks that would have to be eaten. This calculation does not take into considera- 

 tion the elimination of thallium during the period of sickness of the ducks or the 

 excess of lethal dose taken, 



It has been shov/n experimentally that in two days ducks may eliminate 50 

 percent of the thallium sulphate taken. The number of eviscerated ducks a man 

 would have to eat to obtain a lethal dose, therefore, would be many more than 67.5, 

 the exact number depending upon the degree of elimination (135 ducks in the case: 

 of a 50 percent elimination) . 



Observations on mammals given different dosages have indicated that one- 

 sixth the fatal dose v/ill produce symptoms of poisoning, whereas one-eighth will 

 not. To exhibit any symptoms of poisoning, then, a man would have to eat at one 

 meal 15 to 23 eviscerated ducks that had eliminated 50 percent of the poison. As- 

 suming that man also would eliminate 50 percent or more of the poison ingested, 

 and recognizing the cumulative effect of thallium, one sees that he would have to 

 eat tv;o or more ducks a day for 135 days (or considerably longer than the legal 

 duck-shooting season) to take a lethal dose, and that would mean two or more ducks 

 a day for 16 to 23 days before he would even show symptoms of poisoning. 



It can thus be seen that if ducks, or any other birds mentioned, should eat 

 grain poisoned v/ith thallium sulphate exposed in rodent control, and then if these 

 birds later should be eaten by man, the danger from secondary poisoning would be 

 practically nil. 



