POWERS OF RESISTANCE. 233 



in Roux's tubes with 5 per cent glycerine in water during 

 the first period of sterilisation. In the case of the decoc- 

 tions used by Sander, as in glycerine broth, the growth 

 forms a wrinkled membrane on the surface. 



The optimum temperature for growth is 37 to 38 C. 

 Growth ceases above 42 and usually below 28, but on 

 long-continued cultivation outside the body and in special 

 circumstances, growth may take place at a lower tempera- 

 ture, e.g., Sander found that growth took place in potato 

 broth even at 22 to 23 C. 



Powers of Eesistance. Tubercle bacilli have consider- 

 able powers of resistance to external influences, and can 

 retain their vitality for a long time outside the body in 

 various conditions. In this respect they resemble bacilli 

 which are known to possess spores, and this is really the 

 chief argument in favour of the presence of spores in 

 tubercle bacilli, though their resisting power is considerably 

 less than that of most spore -containing bacilli. Dried 

 phthisical sputum has been found to contain still virulent 

 bacilli or their spores after two months, and similar results 

 are obtained when the bacilli are kept in distilled water for 

 several weeks. So also they resist for a long time the action 

 of putrefaction, which is rapidly fatal to many pathogenic 

 organisms. Sputum has been found to contain living 

 tubercle bacilli even after being allowed to putrefy for 

 several weeks (Fraenkel, Baumgarten), and the bacilli have 

 been found to be alive in tubercular organs which have been 

 buried in the ground for a similar period. They are not 

 killed by being exposed to the action of the gastric juice for 

 six hours, or to a temperature of -3 C. for three hours, 

 even when this is repeated several times. It has been 

 found that when completely dried they can resist a tempera- 

 ture of 100 C. for an hour, but, on the other hand, exposure 

 in the moist condition to 70 C. for the same time is usually 

 fatal. It may be stated that raising the temperature to 

 100 C. kills the bacilli in fluids and in tissues, but in the 

 case of large masses of tissue care must be taken that this 

 temperature is reached throughout. They are killed in less 



