BUEEAU OF ANIMAL INDUSTRY. 139 



cattle, proved amply sufficient to prevent the transference of tubercu- 

 losis from one stable to the other. The doors and windows of the 

 stables facing the narrow avenue were open during warm weather 

 and were not screened or made dust proof or fly proof. This ex- 

 posure test continued for about 6 years. An experiment is still in 

 progress in which a separation of only a few feet between small 

 fields or paddocks occupied respectively by tuberculous and healthy 

 (tattle in proving sufficient for the protection of the latter against 

 infectious material from the former. 



What can be accomplished by cleanliness in the fight to control 

 and eradicate tuberculosis among domestic animals is shown by the 

 following test: A healthy herd of cattle was moved into and per- 

 mitted to remain a year in a stable which had been occupied for 

 5 or 6 years by a large herd of tuberculous cattle. Not one case of 

 tuberculosis developed among the healthy cattle. The treatment this 

 stable received after the removal of the tuberculous and before the 

 installation of the healthy herd was limited to a thorough cleaning. 

 While it is not justifiable on the basis of this test to advocate the 

 abandonment of the use of strong germicides to disinfect stables 

 which have been occupied and infected by tuberculous cattle, the need 

 for cleaning up thoroughly before germicides are used can not be too 

 strongly emphasized. Probably a thorough cleaning will not prove 

 sufficient in all cases. 



During the year additional tests proved that tuberculosis does not 

 seem to spread seriously among hogs through the exposure of healthy 

 to tuberculous hogs, and experiments in which tuberculous sows were 

 bred indicate that it is safer for a pig to be the offspring of a tubercu- 

 lous mother than to be exposed to the manure of a tuberculous cow. 

 Though hogs are frequently attacked by tuberculosis, they are not 

 important agents for the perpetuation of the disease, which would 

 almost certainly cease to exist among them if constant accretions of 

 tuberculous material from cattle did not provide for its persistence 

 and increasing frequency. 



Experiments in the treatment of tuberculosis have given no satis- 

 factory or promising results, but are being continued. 



Further studies on the occurrence of tubercle bacilli in the circu- 

 lating blood of tuberculous animals, with special reference to the 

 possibly increased frequency of such bacilli in the blood after tuber- 

 culin tests, have been made. As with our earlier studies, positive 

 results were obtained only with animals affected with more or less 

 generalized tuberculosis which had advanced close to a fatal termina- 

 tion. The injection of tuberculin did not cause a discoverable in- 

 crease of tubercle bacilli in the circulating blood. Many investi- 

 gators have studied this subject, and it is regrettable that the results 

 they report are exceedingly contradictory, which makes additional 

 work urgently necessary. 



Additional investigations regarding the persistence of tubercle 

 bacilli in the tissues of rats which have been exposed to tuberculosis 

 through infected food show that months may elapse before the body 

 of a rat which has eaten infected food is free from tubercle bacilli. 

 Rats permitted to eat tuberculous guinea-pig tissues for only a 

 single day and then removed to a tuberculosis-free environment have 

 repeatedly been proved to harbor tubercle bacilli in their lungs 3 

 months later. 



