126 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



fectious disease results from the stimulation of something Trithin the 

 body by the specific germs of the disease, it is not unlikely that past 

 attempts to produce immunity against abortion disease have given 

 contradictory and discouraging results because the injections of so- 

 called immunizing agents were not properly timed. 



The milk of a cow which has received an intravenous injection 

 of abortion bacilli, in addition to her placentae, often becomes in- 

 fected, and abortion bacilli may be discharged through her vagina 

 continuously for 10 days or more after she has given birth to a calf. 

 These are factoi-s which should be kept in mind in all attempts to 

 induce immunity against the disease w^ith injections of live, virulent 

 cultures of abortion germs. 



TUBERCULOSIS. 



The observations made in the course of the year, like those made 

 at the station for approximately a dozen years, have again empha- 

 sized the great value of scrupulous cleanliness as an aid in fighting 

 the spread of tuberculosis among domestic animals. 



Tests made with domesticated white and wild gray mice proved 

 that their bodies may harbor enormous numbers of tubercle bacilli 

 months after they have been permitted to eat fresh tuberculous 

 material on only one day. The tuberculous material fed in the tests 

 contained bovine types of tubercle bacilli, and it is not known 

 whether human types would give similar results. The mice not only 

 harbor the bacilli in their bodies but expel them freely through 

 their bowels with their feces in gradually increasing numbers. 

 Microscopic preparations of the lungs of mice made six months after 

 they had eaten the tuberculous material often look like smears 

 from pure cultures of tubercle bacilli. Mice which had eaten 

 tuberculous material on only one day were fed three to five months 

 later to a number of hogs, one hog receiving only a single mouse, 

 another two mice, another three, and another four. All four hogs 

 were found to be affected wath tuberculosis approximately three 

 months later, and the disease was either completely generalized or 

 rapidly spreading. 



The tests formed a part of a series of investigations undertaken 

 to find an explanation for the recurrence of tuberculosis in originally 

 tuberculous, cleaned herds of cattle. Such recurrence is not un- 

 common, and is usually attributed to inadequate disinfection of 

 premises or some other cause which can not be accepted as satis- 

 factory in the light of our observations. If the common gray mouse, 

 which is very abundant in our stables, can become a carrier of 

 tubercle bacilli by eating tuberculous material on only a single day, 

 and remain a carrier and disseminator of tubercle bacilli for months, 

 it is urgently necessary in our attempts to disinfect stables which 

 have harbored tuberculous animals to include the extermination of 

 mice. Tubercle bacilli expelled on feed from the bodies of infected 

 mice probably are more dangerous than those which are adherent in 

 masses of dung on the walls of stables or those which have been 

 trampled into the floor. 



Rats, as was pointed out in a previous report, may harbor 

 tubercle bacilli in their bodies for long periods of time after having 

 eaten tuberculous tissues on only one day. The bacilli cause no dis- 



