214 TUBERCULOSIS. 



late years it has been found that growth takes place also on a 

 purely vegetable medium, as was first shown by Pawlowsky 

 in the case of potatoes. Sander has shown that the bacillus 

 grows readily on potato, carrot, macaroni, and on infusion 

 of these substances, especially when glycerine is added. 

 He also found that cultures could be more easily made on 

 potato from tubercular lesions than on glycerine agar. In 

 the case of the decoctions 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 temperature, 

 e.g. Sander found that growth took place in potato broth 

 even at 22 to 23 C. 



Powers of Resistance. 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 the 

 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 temperatue 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- 



