TUBERCULOSIS. 



177 



of chalk. These slowly increase at the edges, and grad- 

 ually form scale-like masses of small size, which under 

 the microscope are seen to consist of tangled masses of 

 bacilli, many of which are in a condition of involution. 



FIG. 56. Bacillus tuberculosis : adhesive cover-glass preparation from a fourteen- 

 day-old blood-serum culture; x 100 (Frankel and Pfeiffer). 



The best method of obtaining a culture is to inoculate 

 a guinea-pig with tuberculous material, allow an artificial 

 tuberculosis to develop, kill the animal after a couple of 

 months, and make the cultures from the centre of one of 

 the tuberculous glands. 



Of course many technical difficulties must be over- 

 come. The tuberculous material used for inoculation 

 may be sputum, injected beneath the skin by a hypo- 

 dermic syringe. The animal is allowed to live for a 

 month or six weeks, then killed. The autopsy is per- 

 formed according to directions already given. A large 

 lymphatic gland with softened contents or a nodule in the 

 spleen being selected for the culture, an incision is made 

 into it with a sterile knife, or a rigid sterile platinum 

 wire is introduced ; some of the contents are removed 

 and planted upon blood-serum. After receiving the in- 

 oculated material the tubes are closed, either by a rub- 

 12 



