RESISTANCE 351 



air-tight closure of the tube. The growth, however, is very slow 



when the culture media have been inoculated from infected animals. 



In later successively transplanted generations the growth is somewhat 



more rapid and the bacilli are not so selective as to the medium in 



which they grow; after the first generation, for instance, they grow 



well on glycerin agar. In the first generation, growth generally is not 



easily recognizable with the naked eye until ten to fourteen days after 



inoculation. The multiplying bacteria form a dry, lusterless, granular, 



more or less wrinkled growth, slightly yellowish in color. Growth takes 



I place best at blood temperature, and does not occur below 30 C. or 



1 above 42 C. The tubercle bacillus is a strict parasite, which does 



I not find in nature the conditions to grow as a saprophyte. Tubercle 



I bacilli have been found in the external world only where they have 



I been sprea^ bv the discharges of tubercular persons or animals. 



Toxic Effects. These depend upon two principal factors, namely, 



(1) the metabolic products of the organism formed during its growth 

 and multiplication in the invaded tissues of susceptible animals, and 



(2) the poisonous substances contained in the body of the bacterium. 

 The latter substances, even after the bacillus is dead and can no 



I longer multiply, cause local abscesses, necrosis, caseation, marasmus, 

 I and elevation of temperature. As has been shown by a number of 

 | authors, including Maffucci, Prudden, Hodenpyle, Strauss, and 

 | Gamalia, dead bacilli injected in small but sufficient quantities may 

 *v produce tubercles with giant cells, but the process remains localized 

 I and tends to heal. 



Resistance. Tubercle bacilli in moist material are probably soon 

 I destroyed by the putrefactive bacteria and the changes they bring 

 about. This was, at least, the view generally held formerly, but 

 | there are now on record some observations which show that this is 

 5" not invariably the case. If tubercular material is placed in water the 

 .. tubercle bacillus may remain alive for a considerable time. The 

 [ bacillus is very resistant to drying out, and may r 'n alive a long 

 I time in desiccated tubercular material, such as s x ,_p**s, and 



'* other discharges; the average is about three months. Direct sunlight 

 | kills the organism if it is spread out in a thin layer, within a few 

 I minutes, but diffuse daylight requires five to seven days. Strauss 

 found that glycerin bouillon cultures with an abundant growth were 

 J. killed if exposed to direct sunlight for two hours Severe cold has no 

 effect upon the bacillus. According to the figures given by Cornet 

 and Meyer in their summary, and obtained from a resume of the con- 

 siderable literature upon the subject, the following periods of time 

 and temperature exposures kill the tubercle bacillus in the moist state: 

 Four to six hours heated at 55 C. 

 One hour heated at 60 C. 

 Ten to twenty minutes heated at 70 C. 

 Five minutes heated at 80 C. 

 One to two minutes heated at 90 to 95 C. 



