DIAGNOSTIC INOCULATION. 219 



imals on test or experimental an- 

 imals in order to determine the pathogenic char- 

 acter of the inoculated material. 

 Diagnostic inoculations are of particular value in the 

 infectious diseases which follow. 



I. Tuberculosis. 



Tuberculosis can be recognized in only a small per cent, 

 of afifected animals by the use of ordinary clinical methods. 



On the one hand only a few symptoms can be determined, 

 on the other hand these symptoms are not characteristic be- 

 cause they also occur in other diseases. The discovery of the 

 tubercle bacillus as the cause of tuberculosis is hardly of any 

 value in the clinical diagnosis of the disease in animals. Mor- 

 bid products from an affected organ (lung of cow) for micro- 

 scopical examination, are difificult to obtain ; the quantity is 

 small and besides is swallowed by the animal as soon as it 

 .reaches the pharynx. But, an opportunity to examine patho- 

 logical nasal secretions, ejections, vaginal discharges or patho- 

 logically altered milk must never be neglected. (See p. 94.) 



Under these circumstances the experimental de- 

 termination of this disease is of great impor- 

 tance. For this purpose we resort to the tuberculin 

 test and to the inoculation of small experimental 

 animals. 



The tuberculin test. Tuberculin is the toxin of the 

 tubercle bacilli, obtained from artificial cultures of the same. 

 The tubercle bacilli are cultivated for six weeks in 5% glycer- 

 ine beef bouillon at 38° C. [100.4° F.] The culture is thea 

 sterilized at 110°C. [230° F.] and filtered through unglazed 

 porcelain tubes. The filtrate is evaporated to one-tenth its 

 volume and thus constitutes tuberculin. After these manipu- 

 lations the tuberculin is absolutely free from germs and there- 

 fore it could never produce tuberculosis. Furthermore, it has 

 no permanent injurious influence on either sick or healthy an- 



