6 BULLETIN 915, U. S. DEPARTMENT OE AGRICULTURE. 



possesses an equally favorable ratio of toxicity, since both fineness 

 and physical texture undoubtedly influence the relative ease of 

 disintegration and rate of solution. 



MINIMUM EFFICIENT CONCENTRATION OF BARIUM CARBONATE. 



Since the experiments already discussed have dealt with the 

 toxicological consideration of barium, there remained to be deter- 

 mined the minimum concentration of barium carbonate in the 

 poisoned bait which would give a high percentage of relatively quick 

 fatalities. For these tests white rats were starved 12 to 24 hours 

 before being fed the poison, to insure an empty stomach and a 

 sharp appetite. The rat is a nocturnal animal and under ordinary 

 circumstances probably would not be deprived of food for longer 

 than 12 hours. A series of 14 rats, therefore, were starved for 12 

 hours and fed at 9 p. m. with the poisoned bait. As there was no 

 marked difference between the results of this series and those of the 

 experiments carried on in the daytime, with respect to both the 

 average food intake and the percentage of fatalities from the con- 

 centration of barium carbonate used, it was concluded that the 

 daytime experiments were valid. 



It was occasionally observed for group tests that the average food 

 intake varied somewhat, although the experiments were tried under 

 as closely similar conditions as possible. For this reason the experi- 

 ments were performed at widely separated intervals to minimize 

 accidental influences and to make the general averages as represen- 

 tative as possible. Sometimes the same rats were used over again, 

 in which instances no evidence was obtained of their having derived 

 any benefit from their previous experience. Because of the fact that 

 the rats used in these tests had been living upon the concentrated 

 type of experimental diet and had accordingly adjusted their appetite 

 or daily food intake, the averages expressed for this type of food 

 might be slightly less than those which would have been secured by 

 the use of a more bulky type of food. Such a possibility, however, 

 is of minor importance, since it would favor the probability of fatal 

 poisoning because of the larger amount of food which might be 

 consumed. 



Several series of starved rats were for an hour offered different 

 types of diet, such as grain, dog biscuit, and soft, mealy food. The 

 last-named food, which consisted approximately of 70 per cent 

 peanut meal, 10 per cent milk powder, and 20 per cent lard, was 

 usually consumed much faster, more of it was eaten before the 

 appetite was satisfied, and less was scattered or wasted. In addi- 

 tion, the rapid consumption of food would occasionally seem very 

 important, since a few rats fairly soon gave evidence of discomfort, 

 due presumably to the relatively quick solution of the barium car- 

 bonate by the acid of the stomach, with consequent irritation. 



