CAUSES OF STERILITY IN THE MULE. 9 



Hayes ('04) in remarking about the matter of sterility of 

 mules says: "Scientific research has amply proved that mules 

 and hinnies are absolutely sterile, although cases are on record 

 of induced lactation occurring in females of this kind. . . . 

 Accounts not infrequently appear in the American and other 

 papers, of mules which are seen suckling young, and the conclusion 

 is at once arrived at that these young are the offspring of the 

 animals that are supporting them, but it may be regarded as 

 perfectly certain that they are merely adopted foals, which by 

 their endeavors to suck female mules have developed in the latter 

 abnormal lactation." 



MATERIAL AND METHODS. 



The material for this study was obtained through the courtesy 

 of my friend, Dr. J. W. Kalkus, professor of histology and path- 

 ology at the State College of Washington, Pullman. Dr. 

 Kalkus made every possible effort to secure the material for my 

 studies and generously placed at my disposal material obtained 

 from three animals. 



The hybrids were about two years old at the time the material 

 was removed from them. It is probable that all three of the 

 mules were by the same sire. The tissue was fixed in Flemming's 

 fluid, and stained with Heidenhain's iron hematoxylin. The 

 sections were cut from five to nine microns thick. 







APPEARANCE OF THE TESTICULAR TISSUE. 



The first noticeable difference in the testicular structure of the 

 mule and the horse is that the seminiferous tubules of the mule 

 are in general much smaller than those of the horse. There is 

 considerable variation among the tubules of the mule. The di- 

 ameter of some tubules is fully twice that of others, and all 

 gradations between the two extremes may be found. The large 

 tubules are characterized by large clear areas in their lumens. 

 This clear space diminishes as a rule in proportion to the di- 

 ameter of the tubules. In most of the small tubules the cells 

 occupy all of the lumen. This structure, however, is not always 

 the case in the respective tubules, for occasionally we find large 

 tubules with solid lumens and on the other hand small tubules 

 with clear lumens. 



