Tuberculosis. 109 



of three or four connected end to end. When cultivated on blood-serum 

 the groups tend to form elongated rope-like colonies, having a waving or 

 serpentine outline. 



Staining.— It is characteristic of this baccillus that it absorbs 

 coloring matters very slowly and once stained retains its color 

 with great tenacity. This enables the microscopist to distinguish 

 this amid a mass of other microbes. The opaque particles in 

 sputum or a section of the tubercle is stained by prolonged ex- 

 posure to a warm alkaline solution of an aniline pigment ; it is 

 then bleached by a solution of nitric acid (1:3); it is then washed 

 and slightly stained with a color which will contrast with the 

 first ; finally it is washed, mounted and examined under the 

 microscope. The rod-like bacillus tuberculosis appears stained 

 with the first color while the other bacteria, if any, are stained 

 with the second. 



Biology, Life-history. — The bacillus tuberculosis lives mainly 

 as a parasite in the animal body, but may be cultivated on the 

 ordinary culture media containing 5 per cent, of glycerine and 

 makes the best growth at 100° to 102° Fah. A temperature of 

 158° Fah. for ten minutes is fatal to it (Yersin). Unlike many 

 bacilli this shows no spontaneous movement at any stage of its 

 growth. Its development is slow in any medium, the earliest 

 signs of growth being visible only after ten or fourteen days. 



Vitality. — As it has great power of resistance to the entrance 

 of coloring fluids, so this germ can hold its own for a length of 

 time against destructive agencies. It retains its vitality and in- 

 fecting power for nine to ten months in dried expectoration (Koch, 

 Schill, Fischer, DeThoma). In tuberculous cow's lung, dried 

 and pulverized, it infected Guinea pigs after 102 days. In putrid 

 matter it infected after 43 days (Schill, Fischer) or 102 days (Ca- 

 deac, Malet). It is not destroyed by gastric juice (Baumgarten, 

 Fischer, Falk). 



In sputum it perishes in 20 hours in a 3 per cent, solution of 

 carbolic acid in a saturated aqueous solution of salicylic acid or 

 in saturated aniline water (Schill, Fischer) ; in five minutes by 

 iodoform ether ; in ten minutes in sulphuric ether or mercuric 

 chloride (1:1000) ; in three hours in thymel. It dies in a few 

 hours in direct sunlight, and in five to seven days in diffuse day- 

 light (Koch). In an ordinary room it gradually weakens but 

 remains virulent for at least 2>^ months (Sawiskey). 



