550 APPENDIX 



from rack shelves the cover is sometimes built into the supporting cage framework. 

 The material may be stainless steel, tinned or galvanized iron, aluminium, or various 

 corrosion-resistant alloys. Brass and copper are never used because the mice may be 

 poisoned by the corrosion products of such metals. A food hopper is usually built 

 into or attached to the cover. 



In our colony the cage cover is of hardware cloth (wire mesh) with a reinforcing 

 rod around the edges. The mesh is 4 squares to the inch and the wire is tinned. A 

 lip is formed around the edges of the cover so that when it rests on the top of the cage 

 the depressed central portion is suspended within the walls of the cage. The cover 

 can be easily removed and replaced, is very light, permits adequate circulation of air 

 into the cage, allows some observation of the contents without removal, is easy to clean, 

 and the cost is quite low. This cover also provides support for the water bottle. In 

 some other designs the water bottle may be suspended against the wall of the cage. 

 The cover described has a heavy wire bottle support which holds the bottle at an angle 

 of about 30 degrees. The water delivery tube extends from the bottle stopper into the 

 cage through a hole in the wire mesh of the cover. Bottle supports should be adaptable 

 for various shapes since requirements for bottles may change more frequently than cover 

 designs. 



Food hopper. — The food hopper (figure 90) should be constructed in such a way that 

 the pellets of food are readily accessible to the mice yet cannot be removed from the 

 hopper in excess of the amount the mice can eat. A hardware-cloth hopper with 3 

 strands to the inch is tolerable for this purpose, but the mice have considerable difficulty 

 in obtaining the food. Wire bar grating or slotted sheet metal is much better. Spaces 

 between wires (or slots) should not be more than 1/4 to 5/16 inches wide. Small 

 mice can squeeze through a 3/8-inch slot, and some of the pellets will also fall through. 



The food hopper may be an integral part of the cover or it may be removable. 

 In some cases the food hopper is attached to the wall of the cage rather than to the cover, 

 although the latter method is preferable. 



In our colony the food hopper is attached to the cover and is located at the end 

 toward the aisle. The hopper is made of slotted sheet metal which is tinned after it is 

 attached to the cover. It is rounded on the bottom, and the sides are inclined slightly 

 to permit stacking. Slots and bars are equal in width ; the slots extend only partway 

 up the side. This prevents the mice from climbing on the hopper and soiling the food 

 with urine and feces. 



Watering devices. — In most colonies bottles are used to provide water for the mice. 

 Usually a metal or glass tube delivers the water. The tube protrudes through a rubber 

 stopper. The end from which the mice obtain water is slightly constricted so that when 

 a drop is lapped a small bubble of air passes into the bottle displacing an equal volume 

 of water. As long as no air leaks past the stopper and nothing breaks the surface tension 

 of the water in the lower end of the tube the water will not run out. Stainless steel 

 tubing is best since water delivery tubes must be sterilized between use. Glass tubing 

 permits visual observation of clogging materials, but are dangerous if broken when 



