8 BULLETIN 915, IT. S. DEPARTMENT OF AGRICULTURE. 



in view, different percentages of barium carbonate were fed. The 

 results of these experiments are summarized in Table 10. 



Table 10. — Efficiency of different percentages of barium carbonate in the diet. 





Barium 



car- 

 bonate 

 in 



rood. 



No. 

 rats. 



Type of experiment. 



No. 

 rats 

 lived. 



Fatalities. 



Date. 



16th 

 hour. 



24th 

 hour. 



48th 

 hour. 



Later. 



Total 



1920. 

 Feb. 7 



1919. 

 Mar.24 



Per 

 cent. 

 5 



5 



5 

 5 



U4 



10 



10 

 10 



Individual, in very large 

 cages. 



Individual, in very small 



cases. 

 do 



6 



5 



6 

 6 





 



(-) 

 ( 2 ) 



2 



1 



1 



1 



6 



1 



2 

 3 







3 



1 

 



Per 

 cent. 



Feb . 15 . . 





Mar. 8 













Total 



5 



44 



23 J 



5 



12 



4 48 





Individual, in very small 

 cages. 



G roup , in very large cages . 

 do 





1919. 

 June 17 



10 



10 

 10 



3 



10 

 10 



2 







5 



(-) 



5 



( 2 ) 



1 



4 

 1 







1 

 1 









 3 





1920. 

 Jan. 27 















Total 



10 



23 



7 





11 



2 



3 



70 





Group, in very large cages. 

 Individual, in very large 

 cages. 





1920. 

 Jan. 27 



20 

 20 



15 

 11 







1 



13 



( 2 ) 



2 

 5 





 3 







2 





Feb. 1 









Total 



20 



26 



1 



20 



3 



2 



96 









i Fed at night. 



2 No observation made. 



About 50 per cent of the rats succumbed when fed 5 per cent 

 barium carbonate. Most of the fatalities occurred after the twenty- 

 fourth hour. On a diet containing 10 per cent, about 70 per cent of 

 the rats died, the majority succumbing within the first 24 hours. 

 Twenty per cent barium carbonate was even more efficient, only 5 

 per cent surviving and a great majority of fatalities occurring within 

 the first 16 hours. 



As already stated, the average food intake at a meal for the aver- 

 age hungry rat is one one-hundredth of the body weight, and from 630 

 to 750 mg. of barium carbonate per kilo may be regarded as the 

 fairly certain fatal dose. When 5 per cent barium carbonate is fed 

 in the bait it would be necessary for all rats to eat 12.5 to 15 grams 

 per kilo, or one-eightieth to one sixth-seventh of their body weight. 

 Some of the rats will do this and die, and a few of those which eat 

 slightly less will succumb. This explains why about 50 per cent of 

 the rats which were fed this diet died. When a 10 per cent barium 

 carbonate bait is fed, a rat must eat one one-hundred-and-sixtieth to 

 one one-hundred-and-thirty-third of its body weight, or 63 to 75 per 

 cent of a meal of average size. A 70 per cent mortality on this concen- 



