PRINCIPLES OF VETERINARY SURGERY 137 



difficulty of staining, and then the subsequent difficulty of 

 decolorizing, is a property belonging to the tubercle bacillus 

 alone. It can be stained with watery or alcoholic solutions 

 of anilin dyes, but special and more effectual methods are 

 now in general use. Koch stained it with an aqueous solu- 

 tion of a basic anilin dye, — a little potassium hydrate as a 

 mordant, — then after washing with water, counterstained 

 with vesuvin. Ehrlich improved the method by using pure 

 anilin instead of potassium hydrate, and then decolorized all 

 the other tissues except the bacilli with a strong mineral 

 acid. This latter method is said to be the best one for stain- 







^<)|r% 



Fig. 14. 

 Bacillus Tuberculosis. (Pure Culture.) 



ing the tubercle bacillus. This micro-organism has been so 

 well studied that many special manipulations are used in 

 dealing with it under the different conditions with which it 

 is encountered. For these special processes the reader is 

 respectfully referred to more elaborate works on general 

 pathogenic bacteriology. 



Diagnosis. — Tuberculosis in animals is diagnosed by 

 three special effectual methods; — (i) By microscopic exam- 

 ination of the elements in the lesions; (2) By animal inoc- 

 ulation; and (3) By the tuberculin test. 



I. Microscopic examinations are made by mounting 



