174 
PRINCIPLES OF BACTERIOLOGY 
appearance. The tubercle bacillus is an aerobic organ¬ 
ism. 
IV. Destruction 
Dry heat (100° C.) will be resisted for one hour. The 
tubercle bacilli are resistant to cold and very resistant 
to drying; in sputum the bacillus remains alive for two 
or three months. A 5 per cent carbolic acid solution 
kills the bacilli in a few minutes, sunlight kills them in a 
few hours. 
Fig. 34.—Tubercle bacilli, human, x 1000 diameters. (Park and Williams 
Pathogenic Bacteria and Protozoa.) 
V. Disease Production, Mode of Infection, Disinfec¬ 
tion and Prophylaxis 
Disease is produced both by inhalation (of infected 
dust) and ingestion (of infected meat, milk, etc.). 
Formation of small nodules, the so-called 11 tubercle/ ’ 
is the characteristic feature of the disease; this may be 
followed by ulceration and cavity formation. Unsani¬ 
tary environment is the best ally the disease has; 
crowded, dark rooms, lack of fresh air, sunlight, nour¬ 
ishing food—is the favorite playground of tuberculosis. 
It is not a hereditary disease; the reason that so many 
children of tuberculous parents develop the disease is 
