RAISING LABORATORY MICE AND RATS 3 7 
RECORDS 
Some system of marking animals for identification and a book in which to 
keep the records are often desirable so that the mice and rats in each litter 
may be distinguished. The type and elaborateness of records will depend 
upon the purpose for which they are used. For some purposes recording only 
sire and dam and date of birth of a litter may be sufficient. In other cases 
more detailed records may be desired. For identification of individual ani- 
mals, systems of ear notching or toe clipping or a combination of both may 
be used. The young may be marked when 15 days of age. A punch of the 
kind used for marking chicks is used for punching the ears. The toes are 
clipped with small scissors. Usually the bleeding is slight. The bloody areas 
may be wiped with a piece of cotton saturated with iodine, mercurochrome, 
or 50-percent alcohol. A numbering system used by the genetics office of the 
Bureau of Animal Industry is shown in figure 3. By this system, numbers 
from 1 to 12,999 may be used as a means of identification. 
“ 
Bek 3\5 
Rr 
7 oa Z 
6: / 
900 NeHOS: 
P00" yoo 500 50 up? 
700 (300 ee 0S Me 
200 20 
600 [60 
400 70 
4000 4/000 
5000 de 2000 
6000 3000 
0,000 7000 
11000 ¢. S &000 
9000 
12000 
Figure 3.—Diagrams of feet and ears 
showing a method of numbering by 
which mice may be identified by toe 
clipping and ear marking. This method 
may be used for rats also. 
DISEASES 
In several instances the mouse and rat are susceptible to the same in- 
fections, though in varying degree. In the following discussion of the more 
common diseases of these rodents, the species affected and degree of suscepti- 
bility are given. 
Bacterial Diseases 
Paratyphoid.—This disease is caused by two species of bacteria, Salmonella 
typhimurium and S. enteritidis, singly, together, or with other organisms. 
Wild mice and rats as well as laboratory stocks of these animals are sus- 
ceptible. Infection takes place usually through the mouth, by eating food 
contaminated by carriers of the organism. Carriers within the laboratory 
colony sometimes serve as a source of infection. Three to six days after 
infection, mice and rats usually develop conjunctivitis and diarrhea. In 
animals dying of the disease, the viscera are congested and the liver, spleen, 
and mesenteric lymph nodes are enlarged. The intensity of these conditions 
depends largely on the duration of the disease. Mortality may exceed 75 
