Xatural Infection. n\r 



found the expressed i.mscle juice of two out of 15 tuberculous cows infectious 

 Kastners arrived at negative results in all cases as long as he confine,! his ex -eri- 

 tliatweie passed for beef. However, when he turned his attention to 7 cows, 6 

 proceed ^,1. r^ condemned on account of advanced generalized tuberculosis, 'he 

 pioduc^d positive results. According to this view, meat may contain bacilli when 



lesions do not produce infection. Swierstra found bacilli in the muscle juice of 

 Bonier? fnn.rr ^"^«^. ^ ont oi 8 swine affected with advanced tuberculosis. 

 Bongeit found the muscle juice virulent in 5 out of 13 cattle affected with softened 

 ubercu ous foci Hoefnagel arrived at negative results in cases of advlnced chronic 

 tuberculosis. ^^^^^^^^^^'^^ obtained only one positive result of aciS SHuaiy 



vp^nif Jli'^'''? *^^* -^^'^ ^^®'\'°^ ""^ "'^^* ^^^"^ tuberculous animals produced positive 

 Giiithef H^^ the tubercle bacillus (Gerlach, 



vl uf 'iJf,""! • „„^°':P '''V}^^y «^^y t¥ r,«P«rt« of Forster & Brown give positive 



resuts whHe those of Galtiei^^ No^ard -^^a-i^e^ F L^^l^^ie ^; '^^ 

 yT:Y %'^' 'V'^''' ^°'' of Perroncito ^hich had been negative w hoi excep on 

 Vander Sluys also was unable to infect pigs by means of fee.ling large quantities 

 of muscle from animas affected with advanced tuberculosis, having iSuedon'v 

 ^ the musdes"' '"' ^° ''"* '^'' '"^^ ''^ "^^^^^"^ tuberculous ofgins and bones 



Natural Infection. Observations in regard to the occur- 

 rence and dissemination of tuberculosis point to the fact that 

 under normal conditions tuberculosis is transmitted only after 

 prolonged exposure to the contagion, or after repeated infection 

 with the virus. It seems that a single light infection usuallv 

 produces only_ a local tuberculous lesion which terminates iii 

 recovery and m addition increases the resisting power of the 

 individual to the disease. In other words, it produces a certain 

 temporary immunity., (For further information see chapter on 

 Pathogenesis. ) '■ 



In the vast majority of cases infection occurs through the 

 medium of ingested food or of inhaled air 



, In alimentary infection the milk of diseased animals fed 

 jI Sf?n 'f f • IJ tlif.yo^^^^.^'is of the greatest importance. 

 In addition to this the skim milk obtained from skimming sta- 

 tions also plays an important role in the dissemination of the 

 disease. Skim milk is^ particularly infectious when the slimy 

 i^esidue which collects m the separator bowl is added to it, as 

 this shme contains large masses of tubercle bacilli when infected 

 milk IS centrifuged (Kjerrulf). 



tim.t7ll"r''*'r!?''' -^ ""^^ containing tubercle bacilli bears an in- 

 ornate relation to the occurrence of tuberculosis in swine which are fed 

 with skim milk furnished by skimming stations. 



exclu|Sy;3^%IS,^Ss^1- l^^^i^^l^^^ ^ ^^/H,^^ 

 Onte'l:: tltTl^TT ^1^ ''' -r i wereTibertlol, \l'at 'ifc^OOoT^: 

 general use for the fpplf.l f sknn milk from skimming stations came into 

 35mn77 «wn tf/^'^'^'ing of swine, the percentage increased to 2.05%. Of 

 eenta^e of T, bprcl 7''" '^^l^^^'r^^ ^19,309 were tuberculous. Thus the per- 

 o^!,fof 7 tuberculous swme has increased five thousand fold (Salmon) The 



In ie''abX?rs If't^Yh''' TT '" *^^ ^°^*^^ ^^^^.s exLeds $3 000,000. 

 inloTol?^ nf Iiil 1?. "? (Amsterdam, Rotterdam) the disease is observed 

 n 15 to Ts^ nl slaughtered swme; m Denmark the disease was formerly present 

 (Pederson) Tn ?tl ''"'"' ' ^°. ^^P^l^^gen 20% of all swine were infected 

 (Pederson) , in Germany some shipments averaged 50 to 60%, and in Hamburg 



