358 THE BACILLUS OF TUBERCULOSIS 



hours. The mixture is then somewhat triturated and definite amounts 

 are placed in small glass tubes. These either contain five or twenty 

 immunity units (J. E.). 1 One immunity unit (J. E.) is equal to 

 0.004 gram dry tubercle bacilli. It is the dose used for the first 

 inoculation of young cattle, while a dose of 0.02 gram or 5 immunity 

 units is employed for the second inoculation, which follows the first 

 after an interval of twelve weeks. The vaccine is prepared from the 

 dry bacilli by mixing the contents of the tubes with sterile physiologic 

 salt solution, so that 5 J. E. are mixed with 10 c.c. ; 20 J. E. with 40 c.c. 

 salt solution. For the first inoculation 2 c.c. of the salt solution 

 bacilli emulsion are used; for the second inoculation after twelve 

 weeks 10 c.c. of the emulsion. Only healthy animals with a normal 

 temperature should be inoculated. The inoculation is made into the 

 jugular vein. It is hardly necessary to point out that the mixing 

 of the dry bacilli and the injection of the emulsion must be done 

 under all possible aseptic precautions. 



Weber and Titze who have employed the von Behring method of 

 cattle immunization believe that the immunity conferred by it does 

 not last over two years. Smith vaccinated 35 calves, weighing from 

 58 to 284 pounds, with seven different human and three attenuated 

 bovine cultures, and from his experimental work he draws the follow- 

 ing conclusions: 



1. Vaccination of calves with the human type of the tubercle 

 bacillus is harmless. Cases in which injuries are said to have resulted 

 from it may have been due to other concomitant affections, among 

 which pneumonia is probably the most common. Persons trying 

 vaccination should first assure themselves that the culture they 

 intend to use belongs to the human and not to the bovine type of the 

 bacillus. 



2. Vaccination with the human type of bacillus leads to a relatively 

 high resistance to fatal doses of the bovine bacillus. 



3. Vaccination with carefully tested attenuated bovine bacilli may 

 be as efficacious even in a single injection as the double vaccination 

 with human bacilli. Such vaccination may be less dangerous to 

 man than when human bacilli are used. 



4. The immunity conferred by vaccination, as hitherto practised, 

 does not appear to be satisfactory as regards degree or duration. 

 More evidence is needed with regard to these points. The herds of 

 large public institutions are well adapted to decide these questions 

 if vaccination is thoroughly applied, and the animals supervised by 

 properly trained men. 



5. Insufficient immunity following vaccination may prove dangerous 

 in giving rise to mild cases, after ordinary exposure in infected herds, 

 which tend to discharge tubercle bacilli from small foci in the lungs. 



1 The term immunity unit (J. E.) as used in connection with the bo vo vaccine of von Behring 

 differs in meaning from the identical term as used to express the immunizing value of diph- 

 theria or tetanus antitoxins. 



