RAISING LABORATORY MICE AND RATS 5 
always greater in a male than in a female of the same age. In animals 21 
days of age the developing scrotum and buttonlike appearance of the genital 
papilla may serve to distinguish the male. 
Care and Management 
CAGES 
The rat will generally gnaw soft materials; consequently metal cages are 
the most satisfactory for housing these animals. Cages about 20 inches square 
and 12 inches high with removable screen bottoms and dropping trays are 
satisfactory for maturing and adult animals (fig. 2, right). However, wire 
floors are not suitable for young animals from birth up to weaning age. 
Pregnant females should be transferred to metal cages which may be some- 
what smaller. These cages should contain litter such as wood shavings or 
Figure 2.—Two types of cages used for rats. The cages at the left have no bottom, but are 
set in a pan 11/4, to 2 inches deep. This pan is bedded with shavings, sawdust, or other 
absorbent material. When the pan needs cleaning, the cage is lifted to a pan of fresh 
bedding material. The cages to the right have wire bottoms, and the droppings fall 
through to the pan underneath, which contains absorbent material. The pan may be 
removed for cleaning. The sides and back of this cage are of solid metal. Record cards, 
held by clips, slide into rectangular holders on the door. 
sawdust to absorb moisture and provide nesting material. The practice in 
some laboratories is to use this type of cage altogether, but the screen- 
bottom type with tray underneath to catch the droppings is more convenient 
to clean, as removable paper can be placed in the tray. Breeding rooms 
should be well ventilated but free from drafts. Temperature should be 
maintained at 70° to 80° F. and preferably as close to 75° as practicable. 
Water bottles and feed cups used for rats are not materially different from 
those used for mice. : 
In handling rats, it is well to wear gloves heavy enough that the rats can- 
not bite through, or to use tongs or forceps. Rat bites may be painful and 
a source of serious infection unless these precautions are taken, nr 
