434 THE TUBERCLE BACILLUS GROUP 



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 two years 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. 1 



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 four pounds of sulphur to 1000 cubic feet in a moist atmos- 

 phere, or by evaporating 500 c.c. 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 

 infectious for some time. In order to determine that tubercle bacilli 

 are killed it is necessary to inoculate the material containing them 

 into guinea-pigs, the guinea-pig being far more sensitive than artificial 

 media for this purpose. Theobald Smith 2 has shown that it takes at 

 least 1500 times as many tubercle bacilli to infect artificial media 

 as it does to infect a guinea-pig. It must be remembered that even 

 killed tubercle bacilli, as Prudden and Hodenpyl 3 have shown, produce 

 tubercles in guinea-pigs, but that these tubercles are not transmissible 



1 Theobald Smith, Jour. Exp. Med., 1899, iv, 233. 



2 Jour. Med. Research, 1913, xxviii, 91. 



3 New York Med. Jour., Jun e6, 1891, p. 20. 



