No. 7. DEPARTMENT OF AGRICULTtJRE. 125 



amount of the culture film to a given quantity of sterile, normal salt 

 solution. The culture film is broken up, so that the tubercle bac- 

 illi will not occur in clumps but will be equally distributed through 

 the fluid, by agitating the suspension in a flask with metal balls. It 

 will be seen therefore, that the vaccine consists of living tubercle 

 bacilli of human type floating in normal salt solution. This material 

 is injected into the jugular vein of the calf that is to vaccinated. 

 After from six to eight weeks a second vaccination is made and 

 after this a third following a like interval. Each dose is larger than 

 that preceding it. No preceptible change occurs in the animal as a 

 result of the first vaccination. The second vaccination usually 

 causes a passing fever, that disappears in a day or two leaving the 

 animal in a normal condition, the fever following the third vaccina- 

 tion is usually even lighter than that following the second. During 

 the process of vaccination and for six weeks thereafter the animal 

 should be protected from exposure. We have not always done this 

 in our experimental work and have had some entirely successful re- 

 sults when this precaution was not observed. But it is considered 

 to be safer to adopt this plan. Six weeks after the third vaccination 

 the animal may be exposed to infection by placing it in infected 

 premises and allowing it to associate with tuberculous animals and 

 it will remain sound. Of course, as has been stated, if the condi- 

 tions of exposure are excessively severe it may be well to give more 

 immunity by vaccinating a fourth time. But this is not neces- 

 sary in any fairly well managed herd and if the conditions are above 

 the average for infected herds it is probable that two vaccinations 

 will suffice. We now have some experiments in progress that will 

 throw additional light on this point. 



''While it is possible to vaccinate too little, it is also possible to 

 vaccinate too much. That is, if the doses are too large and too fre- 

 quently repeated the resistance of an animal may be diminished 

 rather than increased, and especially if exposure occurs during or too 

 soon after vaccination. 



"The duration of immunity is a most important question and is 

 one upon which data is being gathered slowly. Some of our experi- 

 ments seem to indicate that the duration is dependent in some de- 

 gree on the amount of vaccination. For example, two yearlings 

 were vaccinated in exactly the same manner; each received two vac- 

 cinations, the last on January 2Gth, 1904. Both were exposed Febru- 

 ary 16th 1904. One was killed December 6th, 1904, after 9J months' 

 exposure and was quite free from tuberculosis. The other was killed 

 December 80th, 1905, after 22^ months' exposure and was found to 

 have comparatively small lesions of tuberculosis in two lymphatic 

 glands, a post pharyngeal and a mesenteric. Two other yearlings 

 in the same experiment was vaccinated three times, they were killed 

 January 21st, 1906 after 22 months of severe exposure and were 

 quite sound. Two unvaccinated cattle exposed with these died of 

 tuberculosis, one after 22 and the other after 28 1-8 months of expo- 

 sur. Another unvaccinated control was killed after it had been ex- 

 posed eight months and it was found to be extensively tuberculous, 

 lesions being present in the bronchial and mediastinal lymphatic 

 glands and in the lungs. 



"The following case is very interesting on account of the informa- 

 tion it furnishes as to the duration of immunity. The animal was a 



