BACTERIUM TUBERCULOSIS 145 



under or upon the skin is the stimulation of the tuber- 

 culous disease by the introduced toxin, and the out- 

 pouring from the tubercles of more of their own poison. 

 No reaction of any sort follows the administration of 

 tuberculin to persons free from tuberculosis. 



Morphology and General Characteristics. The tubercle 

 bacillus is a true parasite, that is, it does not multiply 

 in nature outside the animal body. It is a rather 

 large organism, about TOTTOT mcn wide and from 

 YolToir to 5~oVo inch long. It may be straight or slightly 

 bent, usually single, but also in pairs. It is non- 

 motile, and produces no spores. It stains with con- 

 siderable difficulty, owing to its thick cell wall. There 

 is much fatty and waxy matter in the tubercle bacillus 

 which gives it its resistant power. It grows upon 

 laboratory culture media very slowly. For this 

 reason it must be obtained in as pure a condition as 

 possible. Cultures are best made from the lesions in 

 guinea-pigs. For its growth this organism requires 

 the addition of glycerin, blood serum, or egg to the 

 ordinary nutrient broths and jellies. It will grow only 

 at body temperature, and not at room temperature. 



It is killed by an exposure to 60 C. or 142 F. in 

 thirty minutes, to 70 C. or 160 F. in ten minutes, 

 and at 95 C. or 200 F. in one minute in watery 

 suspension. Dry heat at 100 C. or 212 F. requires 

 about one hour. The organisms resist drying in the 

 dark for considerable periods. Direct sunlight kills 

 them if in thin layer or small clumps, within four 

 hours. Diffused light requires two weeks for their 

 destruction. Sputum protected from direct sunlight 

 may contain living bacilli possibly for one year. Five 

 10 



