426 VeteHnary Medicine. 



Such small herds, in which all become early infected, and in' 

 which there is no further opportunity for the infection of sus- 

 ceptible animals (cowsnot yet infected, heifers in first gestation, 

 new purchases) , furnish a better opportunity than do large herds,, 

 to trace the acquirement of tolerance. 



In a question of this kind, one must allow for variations in the 

 different types of abortion caused by various microbes, but in the- 

 forms with which we are familiar in Europe and America, the 

 acquired tolerance of the individual can be counted on with great 

 confidence. It has indeed been largely traded upon by purveyors, 

 of antiabortion nostrums who promise to cure the individual cow,, 

 to which alone their drugs are administered. Two evils result :; 

 the stock owner's money is paid for that which, unaided, nature 

 would have accomplished for him ; and attention is withdrawn 

 from the real necessity of the case, the prevention of the infection 

 of freshly introduced animals. The nostrum vender thus secures- 

 for himself a growing market, as the yearly production of fresh 

 cases in the same herds, appears to demand a constant use of the 

 agent which appeared to work so well in the earlier ones. 



Immunized animal still infecting. The cow that no longer 

 aborts is not, therefore, a safe member of a herd. As an indi- 

 vidual animal she has become resistant to the pathogenic influ- 

 ence of the germ, she is invulnerable to it to the extent that she 

 no longer aborts, but her system and generative passages have ac- 

 quired no such active bactericidal power over the microbe as to- 

 lead to its speedy destruction. The genital passages, once col- 

 onized, continue to be a field of growth of the bacillus long after 

 its power to cause abortion in that particular animal has passed. 

 Analogous cases can easily be quoted from the field of pathology.. 

 The horse that has apparently recovered from dourine still con- 

 veys the disease to others with which it has sexual congress ; the 

 recovered syphilitic person is by no means eligible for marriage ; 

 the recovered pig continues to carry the infecting swine-plague 

 bacillus in its air passages. In short, it iS the rule that the im- 

 munized animal can with safety to itself carry a germ that readily 

 infects its non-immunized fellows. 



In the case of infectious abortion this is one of the most dan- 

 gerous elements, as the apparently healthy recovered cow receives 

 no attention in the way of separation and disinfection, but is- 



