TUBERCLE BACILLUS 471 
monium salts of the simpler dibasic acids as sources of nitroojeu. 
The tubercle bacillus grows iu milk, producing a gradual solution of the 
casein. 1 
The tubercle bacillus is aerobic,' although it will develop very slowly 
anaerobically. Its temperature range is rather limited, the organisms 
growing between 30° C. and 42° C, with an optimum temperature 
of 37° C. Growth below 35° C. is slow. Tubercle bacilli are fairly 
resistant to drying, naked germs being killed by dry heat at 1()()° C. 
only after forty-five minutes. With moist heat an exposure to ()0° 
r. kills them in thirty minutes, 65° C. in fifteen minutes, 70° (\ in 
five minutes, 80° C. in one minute, and 100° C. in one-half minute. 
The organisms enclosed in mucus are much more resistant, dry heat 
(100° C.) killing them only after an exposure of from two to three 
hours, 70° C. after seven hours, and 60° C. after ten hours. In sterile 
water the organisms may remain alive for over two months. They 
are quite resistant also to putrefaction. Instances are on record 
where tuberculous lungs have been buried for six months and yet 
contained virulent organisms. Schottelius^ claims that a tuberculous 
lung buried a whole year contained virulent tubercle bacilli at the end 
of that time. 
The thermal death-point in milk is 60° C. for thirty minutes. There 
is a source of error in determining the thermal death-point of the 
tubercle bacillus or of any other organism in milk. If the experiment 
is carried out in milk which is not enclosed in such a manner as to 
prevent surface evaporation the results are inaccurate; the scum 
which forms on the surface of the milk as the result of evaporation 
contains casein and salts; they are non-conductors of heat and protect 
the organisms so that they apparently resist a much higher tempera- 
ture than would otherwise be the case'' 
Tubercle bacilli in sputum are killed in twenty -four hours by mixing 
the sputum with an equal volume of 5 per cent carbolic acid. Mer- 
curic chloride is not suitable for this purpose because it precipitates 
mucus, forming a compound with it which renders its germicidal 
action nil. Rooms containing tubercle bacilli may be disinfected either 
by burning 4 pounds of sulphur to 1000 cubic feet in a moist atmos- 
phere, or by evaporating 500 cc. of formaldehyde to every 1000 cubic 
feet under the same conditions. The room should not be opened up 
until after eight hours have elapsed. 
Direct sunlight kills tubercle bacilli even when they are enclosed 
in sputum, but the rapidity with which they are killed depends some- 
what upon the season; a longer exposure is required in winter than 
in summer. Sputum exposed out of doors in indirect light may remain 
1 Klein: Centralbl. f. Bakteriol., 1900, 28, 111. Monvoisin: Compt. rend. Acad. 
Sci., October, 1909, 26; Rev. de med. veterin., 1910, 87, 16. Mossu and Monvoisin: 
Compt. rend. Soc. de Biol., 1907, 73, 156. Kendall, Day and Walker: Jour. Am. Chem. 
Assn., 1914, 26, 1959. 
- See Novy and Soule: Respiration of the Tubercle Bacillus, Jour. Infec. Dis., 1925, 
36, 16S, for very complete discussion. 
^ Centralbl. f. Bakteriol., 1890, 7, 265. 
^ Theobald Smith: Jour. Exp. Med., 1899, 4, 217. 
