54 HELEN DEAN KING AND HENRY H. DONALDSON 



chiefly ovarian or mammary. The ear infection, mastoiditis, 

 rendered it necessary to dispose of four other females, while 

 seventeen had to be killed because they had lung disease in 

 an advanced stage. 



Some years ago, in collaboration with my colleague, 

 Dr. J. M. Stotsenburg, autopsies were made on a considerable 

 number of albino females, from eight to twenty months old, 

 that had never cast young although they were apparently in 

 good physical condition. These autopsies showed that, in the 

 majority of cases, sterility was due to abnormal or diseased 

 conditions of the reproductive organs. In some females the 

 ovaries were very small and obviously immature; in other 

 females the ovaries were abnormally large, much lobulated, 

 and frequently contained pus; ovarian tumors or cysts were 

 present in other females. A pathological condition of the 

 uterus was the cause of sterility in many cases. In some 

 females the uterus was much congested, the horns containing 

 yellowish nodules of pus ; in others the uterus was very small 

 and anemic. An infectious disease of the oviducts, pyosal- 

 pinx, was found in some instances. In its early stages lung 

 infection does not prevent conception, but it seriously inter- 

 feres with embryonic development. Offspring of infected 

 mothers are usually very small at birth, many of them are 

 born dead, and those that live show low vitality and usually 

 die at an early age. As this disease advances, it leads to 

 complete sterility. It seems probable that infertility in fe- 

 male rats is due chiefly to diseases affecting the reproductive 

 organs or to the devitalizing effects of lung infection. Im- 

 potency in males is comparatively rare, and when found is 

 caused mainly by diseases, such as lung infection, that lower 

 the vitality of the individuals. 



As previously stated, if gray females were in good physical 

 condition they were kept until it was evident that breeding 

 was at an end. Autopsies made on old females that had not 

 cast young for several months frequently showed that a state 

 of pregnancy existed, but that the embryos were in the process 

 of being resorbed. It is evident, from this finding, that ovula- 



