BACTERIUM TUBERCULOSIS 139 



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 diagnostic 

 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 

 culture, be injected under or rubbed into the skin, a char- 

 acteristic reaction occurs. The subcutaneous injection of as 

 small a quantity as 5 milligrams or about YG minim 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 modifications of this skin test in practice, 

 but the principle is the same in all. Tuberculin, purified 

 by precipitation with alcohol, can be obtained in powder 

 form, a solution of which has the property of calling forth a 

 reaction in a tuberculous person. This refined product is 

 used in the conjunctival test by dropping a small quantity 

 into the eye. If tuberculosis be present a congestion and 

 discharge will appear in the conjunctiva within forty-eight 

 hours. 



It is claimed by many that all adults have some tuber- 

 culosis in their body, acquired during childhood, which has 

 remained quiet or has healed completely, but which has left 

 their blood in such a condition that a tuberculin reaction will 

 appear. For this reason the skin test may be positive in 



