202 BACILLUS TUBERCULOSIS. 



ing from 4 to 6 per cent, of glycerin. The surface of the 

 liquid is inoculated with a pure culture of the tubercle bacil- 

 lus and placed in an incubator for from six to eight weeks, 

 when development ceases. The thick dry pellicle which has 

 formed on the surface of the liquid sinks. The bouillon is 

 evaporated over a water-bath to one-tenth of its volume, and 

 filtered through porcelain, gravel, or sterilized filter-paper. 

 The filtrate is tuberculin. It contains from 40 to 50 per 

 cent, of glycerin and keeps quite well. 



Koch believed that it w r as possible to produce immunity 

 against the toxin but not against the bacillus. Tuberculin is 

 not bactericidal. Tuberculin induces coagulation-necrosis in 

 the vicinity of the tubercular lesion, and interferes with the 

 further development of the bacilli, many of them dying. The 

 vitality of the tissue-cells surrounding the tubercular spot is 

 also seriously diminished; there are hypersemia and degener- 

 ation of the tissue, and finally absorption of the poisons into 

 the blood, with consequent liability of spread of the process 

 to other parts of the body. 



As a diagnostic agent tuberculin is of great value. The 

 subcutaneous injection of tuberculin in doses of from 1 to 5 

 milligrams into a non-tubercular individual is not followed by 

 appreciable reaction. A like dose injected into a tubercular 

 patient is always followed by a decided reaction, such as 

 increased temperature, headache, lassitude, and at times nausea 

 and vomiting, and chilliness or distinct chills and rigors. In 

 doubtful cases tuberculin is probably the only means at our 

 command for making a positive diagnosis. It is advisable to 

 begin with a very minute dose, in order to ascertain the sus- 

 ceptibility of the patient. Subsequent doses can be regulated 

 accordingly. 



Before injection the temperature-standard of the patient 

 should first be determined. Therefore the temperature is 

 taken every two hours from 4 o'clock in the morning to 

 10 o'clock at night, for two or three days prior to the use of 

 the tuberculin. In this way we obtain both the highest and 

 lowest temperature-record of that person, and this tempera- 

 ture-record is a valuable aid in determining the degree of 

 reaction, if any. 



