BACTERIUM TUBERCULOSIS 155 



re"d bacilli, which are easily distinguished under the 

 microscope. 



Sometimes the germs are present, but cannot be 

 found by staining. Some of the material is then 

 introduced under the skin or into the peritoneal 

 cavity of guinea-pigs. If tubercle bacilli be present, 

 evidences of the disease will appear in these animals 

 in from two to five weeks. The bacilli can be found by 

 staining smears from the tubercles. Agglutinins are 

 formed in tuberculosis, but the clumping test is of 

 little value. 



The tuberculin reaction is a very important diag- 

 nostic measure. During its growth on artificial media 

 in the laboratory, the tubercle bacillus develops its 

 endo- and extracellular toxins. If these poisons, 

 called ^tuberculin," obtained by removing the living 

 organisms from a fluid cujture, be injected under or 

 rubbed into the skin, a characteristic reaction occurs. 

 The subcutaneous injection of as small a quantity as 

 5 milligrams or about yV niinim of Koch's tuberculin 

 will cause a definite rise of temperature and a feeling 

 of general malaise within twenty-four hours. There 

 is besides this a congestion of the tuberculous process 

 in the lung or wherever it may be. The inunction of 

 a drop of this solution into the skin, combined with a 

 slight irritation of the surface, will cause a reddened 

 papule or even a vesicle upon a swollen base to appear 

 within twenty-four hours. There are several modifi- 

 cations of this skin test in practice, but the principle 

 is the same in all. Tuberculin, purified by precipitation 

 with aclohol, can be obtained in a powder form, a 

 solution of which has* the property of calling forth a 



