202 
Journal of Agricultural Research 
Vol. XXXI, No. 3 
EXPERIMENTAL WORK 
Description and Care of Breeding Rats 
The albino rat was used in all the tests reported in this paper. 
The foundation stock for the breeding colony was obtained from 
E. C. Schroeder, in charge of the Experiment Station of the Bureau 
of Animal Industry, United States Department of Agriculture, at 
Bethesda, Md. A continual process of selection and elimination has 
been practiced in breeding the rats, and the colony is healthy, 
vigorous, and prolific. The average weight of mature males is 
approximately 300 grams and of females 190 grams. The number 
of young in a litter ranges from 4 to 16, the average being approxi¬ 
mately 8. The rats, both breeding and experimental, are kept in a 
well-lighted room with a southern exposure; but, on account of 
certain obstructions in front of the windows, only a very few of the 
rats are exposed to the direct rays of ihe sun. 
The following-described ration is at present being fed to the breed¬ 
ing rats, and it has not been modified materially for some time: 
Ration for breeding rats 
Per cent 
Yellow corn_ 27. 5 
Oatmeal_ 20. 0 
Wheat_ 25. 0 
Dried beef_ 15. 0 
Dried egg or egg yolk- 4. 0 
Per cent 
Dried yeast_ 4. 0 
Calcium carbonate_ 4. 0 
Sodium chloride_ 0. 5 
100. 0 
In addition to this ration the rats are given fine-cut cabbage at 
frequent intervals and water. 
System of Testing for Vitamin A 
Young rats weighing approximately 40 grams each and not ex¬ 
ceeding 30 days in age, when they reach that weight are selected for 
the tests. As a rule, four rats are fed each ration. No attempt 
is made to select rats from different litters, and the sexes are ordi¬ 
narily about equally divided. Each rat is weighed at the beginning 
of the test and at regular semiweekly intervals thereafter for a 
period of 90 days, unless the experiment is terminated earlier by 
nutritive failure or by some untoward circumstance. 
Each rat is kept in an individual, cylindrical-shaped cage with 
a separate pan bottom, as shown in Plate 1, A and B. The dimen¬ 
sions of the cage are as follows: The upper part is 1034 inches in 
diameter at the top, 1134 inches at the bottom, and 8 inches high. 
The heavy clip projecting midway on the outside prevents the cages 
sticking together when stacked. A hole in the top allows insertion 
of the glass drinking vessel, which is held in place by a removable 
spring clip on the inside of the cage. The pan bottom is 11% inches 
in diameter at the bottom, 12 inches at the top, and 2J4 inches 
deep. The slight flare to the sides permits stacking. A circular 
screen made of 34“inch mesh galvanized wire, and slightly smaller 
than the pan, is used to protect a circular sheet of heavy blotting 
paper which serves as an absorbent. 
Each cage is provided with a self-feeder ( 3 ) as shown in Plate 1, C, 
which holds approximately 100 grams of feed. By this means an 
accurate record is kept of the feed consumed. 
