52 LABORATORY MOUSE 



typhi murium. If one can possibly spare the mice, it is 

 advisable to kill off each day all sick animals and sterilize 

 the cages at once. Some adult mice are not killed outright 

 by the disease, but they remain carriers of the condition and 

 may do much damage by spreading it. This disease is 

 usually fatal to animals between fifteen and twenty-five days 

 of age. A few recover, and if these are females they may 

 be normal and reproduce, but if they are males they will 

 usually be sterile, due to the fact that the poisonous, diar- 

 rhoeic feces "scald" the scrotal region, causing the forma- 

 tion of scar tissue. The stiff scar tissue prevents the descent 

 of the testicles necessary for fertility. Thus it is advisable 

 in every case to kill all young affected males. If valuable 

 young females are preserved, they should not be kept in the 

 mouse room. 



By the enumeration of the above pathological conditions 

 and insistence upon drastic measures to eliminate disease 

 from the mouse colony, it is not intended to give the im- 

 pression that mice are weak and susceptible to all sorts of 

 sickness, making them difficult to raise in quantity. There is 

 no limit to the number of healthy mice which may be main- 

 tained in a well-tended murarium. Five thousand is not an 

 unusual size of colony for an experimental laboratory. 



Breeding Cages. There are a number of practicable de- 

 signs for successful breeding cages, but the most satisfactory 

 are those which provide adequately for certain requirements 

 peculiar to the mouse. The design of the cage should take 

 into consideration size convenient for handling, space oc- 

 cupied, dry feed, closed water bottles, changeable nesting 

 material, absorption of urine, and ease of sterilization. A 

 mouse cage meeting these requirements has been developed 

 at the Bussey Institution (see Fig. 10). 



The cage is made of galvanized-iron wire netting of 

 ^ inch mesh. The dimensions of the cage are 12 inches long, 

 7 inches wide, and 7 inches high. It rests upon half an inch 

 of sawdust in a galvanized-iron pan 15 inches long, 13| 

 inches wide, and 3| inches deep. Two cages nest side by 



