PHAKMACOLOGY OF THALLIUM 
13 
bait. The sample of thallium compound to be tested was powdered, 
accurately weighed, thoroughly mixed with a weighed quantity oi 
the sieved rat food by a spatula, and finally passed through a 20-mesh 
sieve several times to insure thorough mixing. Concentrations were 
prepared upon the basis of the actual thallium content, regardless of 
the salt fed. The thallium concentration in the finished baits ranged 
from 0.25 to 10 per cent, although 0.5 per cent was commonly used. 
In an effort to standardize the condition of the rats used in 
these tests, all animals (wild or white) were kept under laboratory 
conditions for several days to a month, and fed ordinary laboratory 
rat food. They were then placed in individual cages and deprived of 
food for 12 to 24 hours to insure uniformly empty stomachs and good 
appetites. Water was offered at all times. The rats were carefully 
weighed at the end of the deprivation period, and doses of thallium 
were calculated in terms of milligrams of thallium per kilogram of 
body weight of animals. The determined quantities of bait were ac- 
curately weighed and placed in large glass sponge cups, which were 
introduced into the cages at a stated time. Frequent inspections were 
made, and the rapidity with which the different baits were attacked 
and consumed was noted. The sponge cup, containing any uneaten 
food, was removed after several hours, and the remaining quantity 
weighed, to determine the quantity of thallium consumed. On 
the next day, all animals were returned to the regular rat diet, with 
plenty of water. In general, the animals were kept in individual 
cages for a period of five days. All animals dying within five 
days (occasionally it took a longer time) that showed symptoms of 
thallium poisoning were recorded as dying from the dose consumed. 
The development of toxic symptoms or death was watched; in some 
instances post-mortem examinations were made to determine the 
gross changes produced by the poison. 
The minimum lethal dose was taken as the quantity of thallium 
that caused the death of all test animals, or practically all, within 
the period of five days. Doses somewhat larger than the accepted 
minimum lethal dose must kill all test animals; doses somewhat 
smaller (20 to 25 per cent) killed less than half of the test animals. 
The minimum lethal dose is considered to be accurate within 10 to 
20 per cent, which is the usual range of reaction of test animals. 
FEEDING EXPERIMENTS 
SERIES 1 : C0MME31CIAL THALLIUM-TREATED GRAIN 
A sample of grain and one of a paste containing thallium as the 
toxic ingredient were tested in July, 1924. The grain appeared to 
be medium-sized kernels of wheat coated with a reddish scum. The 
paste was of a greenish hue and had the consistency of lard. Chem- 
ical analyses of these products were not undertaken, as analytical 
methods were not readily available. Count of the grain showed 
that 440 kernels weighed 17.5 grams and that 680 kernels weighed 
27.0 grams, or an average of 25 kernels to the gram. 
Seven wild rats, weighing 78 to 335 grams, were offered weighed 
and counted quantities of the grain at 3.30 p. m., July 25, 1924. 
The uneaten food was removed at 9 a. m. the next morning. All 
animals were alive on the second day ; on the third day after feeding. 
