268 TUBERCULOSIS 



Sander found that growth took place in glycerin-potato broth 

 even at 22 to 23 C. 



Powers of Resistance. Tubercle bacilli have considerable 

 powers of resistance to external influences, and can retain their 

 vitality for a long time outside the body in various conditions ; 

 in fact, in this respect they may be said to occupy an inter- 

 mediate position between spores and spore-free 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 temperature 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 than a minute by exposure to 5 per cent, 

 carbolic acid, and both Koch and Straus found that they are 

 rapidly killed by being exposed to the action of direct sunlight. 



Action on the Tissues. The local lesion produced by the 

 tubercle bacillus is the well-known tubercle nodule, the 

 structure of which varies in different situations and according to 

 the intensity of the action of the bacilli. After the bacilli gain 

 entrance to a connective tissue such as that of the iris, their 

 first action appears to be on the connective-tissue cells, which 

 become somewhat swollen and undergo mitotic division, the 

 resulting cells being distinguishable by their large size and pale 

 nuclei the so-called epithelioid cells. These prolif erative changes 

 may be well seen on the fifth day after inoculation or even 

 earlier. A small focus of proliferated cells is thus formed in the 

 neighbourhood of the bacilli, and about the same time numbers 

 of leucocytes chiefly lymphocytes begin to appear at the 

 periphery and gradually become more numerous. Soon, however, 

 the action of the bacilli as cell-poisons comes into prominence. 

 The epithelioid cells become swollen and somewhat hyaline, their 



