TUBERCULOSIS 139 



remaining clear. The potato culture medium is prepared according to 

 Roux and Globig's method (see Technique, p. 49). In 1882 Koch and 

 Kitasato devised a means of obtaining cultures of tubercle bacilli direct 

 from the sputum of phthisical patients. They washed out the patient's 

 mouth with an antiseptic gargle, and emptied the expectorate into a 

 Petri-dish. One of the expectorated masses of sputum is washed in 

 several changes of sterile water to free the exterior of bacteria ; out of 

 the middle of the washed sputum a portion is removed with the platinum 

 needle, and stroke cultures prepared on the surface of blood serum. 

 The developing cultures exhibit a somewhat different appearance to 

 those cultivated from the bodies of animals; they appear as round, 

 whitish, transparent colonies, but the later generations grow in the same 

 manner as those previously described. The bacilli can be cultivated 

 through many generations for several years without injuring their power 

 of growth, although the older cultures become less virulent. (For Photo- 

 micrograph of specimen from pure culture, see Fig. 49.) 



Vitality. The Bacillus tuberculosis is destroyed by heating for ten 

 minutes at 70 C., one minute at 95 C., one hour at 60 C., and four 

 hours at 55 C. They only resist the action of direct sunlight for from 

 some minutes to some hours, according to the thickness of the growth. 

 Exposed to diffuse daylight they are killed in a week. 



Pathogenesis. None of the domestic animals are immune. The 

 guinea-pig is the most susceptible of all the experimental animals, a 

 very small quantity of tubercle bacilli being sufficient for their 

 infection ; next come the rabbit and the field mouse ; less susceptible, 

 and still far from immune, are white mice and dogs. Young animals 

 exhibit a greater predisposition for tuberculosis than older animals. 

 Typical tubercular lesions are produced in guinea-pigs, rabbits, and 

 field mice by subcutaneous injection, inoculation into the anterior 

 chamber of the eye, intraperitoneal and intravenous injection, or by 

 inhalation of moist powdered tubercle bacilli. 



Susceptible animals infected by feeding with tubercular matter die 

 of abdominal tuberculosis. 



Baumgarten inoculated animals in the anterior chamber of the 

 eye, and in three days found the bacilli in the auricular lymph-glands. 

 Intravenous injection produces a generalized miliary tuberculosis. 

 The experiments of Schiiller are of especial interest in relation to 

 many localized tubercular diseases of man ; he injected tubercular 

 material in a suitable part of an animal, then produced an injury in 

 the region of the knee-joint, and observed that the infection became 

 localized at that point. Dead tubercle bacilli produce pyogenic 

 results ; they are positive chemotactic, drawing the leucocytes towards 



