354 VETERIXXKV r'ATn(.)Lt)t;Y. 



in which the primary tul:)ercle occurs the extension is by con- 

 tiguity. 



In thie majority of the cases of lymphatic extension and in 

 some of the cases of blood extension the Bacterium tuberculosis 

 is inccirporated in and transported by leucoc3'tes. The leucocytes 

 usiidlh" lia\"e sufficient vitalit\- to destroy the incorporated bac- 

 teria Init occasionalh' the leucocytes may l^e destroyed after 

 hax'iuL;- transported the Ijacteria a consideraljle distance. Thus a 

 Bacterium luljerculosis Imm a pulmonarA' tuliercle may be incor- 

 pciratcd h\ a lcucoc}'te and carried to the kidne\' and th.e leuco- 

 CA'le 1)cinq- destroyed the lil^erated bacterium may estal^lish a tub- 

 ercular I(jcus m the renal tissue. The occurrence oi Bacterium tul)- 

 crculLisis in the milk i if cows liaviuL;' no mammar\- tubercular 

 lesiijns as well as the fact that ingestidu of tubercular materia! 

 frcijuentb- causes pulmonar\- tulierculosis, may be due to leuco- 

 c}-tic incorporation and transji' irtation cif the infecting micro- 

 ijrL^ani-m. 



Elimination. — h'roni the sanitary pnint of \-ieA\- it is ahvax'S of 

 cunsiileralile iniportance to kunw the channels or avenues 

 llircugh y-hich infeetnius agents are discharged in order that thcA' 

 may ije destn i_\-ed. Tiilierculi isis affects all tissues and tlie B>ac- 

 terium tulierculosis may nnt lie eliminated fmni the affected ani- 

 mal cir it ma}- be discharged in one or mure of ilie secretions or 

 excretiMus. It has been iletermined b\- the llepartmcnt df Agri- 

 culture that abriut -lo jier cent of tuljcrcular cattle eliminate the 

 Bacterium tuberculosis in their feces. The same in\-estigators 

 alsd fnund. in a limited mmiljer of dairies, that about 2r, per 

 cent of tubercular c^ws, regardless of location of the lesions, 

 eliminated the Bacterium tuberculosis in their milk. These are 

 facts of prime importance in adopting means for checking the 

 progress • <r fur sui)pressirin of the disease. The discharges from 

 the resjiiratriry tract of tubercular animals frec|uentlv contain the 

 Bacterium tuberculosis, es]iecially if they haye pulmonary lesions 

 of the disease. The urine and discharges from the female genital 

 organs may be contaminated with the infection. Renal tuber- 

 culosis, howeyer, is not of frequent occurrence and it is not 

 probable that the Bacterium tuberculosis is eliminated in the 

 urine of tubercular animals in which there are no renal lesions. 

 In general the channel of elimination of the bacterium tuber- 

 culosis depends largely upon the location of the lesion. 



Tuberculin and Tuberculin Test. — Tuberculin is a bio-chemic 

 material containing the products and the disintegrated bodies 

 of the Bacterium tuberculosis. It is prepared by growing the 

 Bacterium tuberculosis in glycerine bouillon for a certain length 



