KOCH'S TUBERCLE BACILLUS 327 



occur locally in the lungs, liver, glands, intestine, larynx, bones, 

 kidneys, spleen, and other parts. 



We may summarise the history of the pathology of tubercle 

 thus : 



1794. Baillie drew attention to grey miliary nodules occurring 

 in tuberculosis, and called them " tubercles." 



1834. Laennec described four varieties: miliary ; crude; granu- 

 lar; encysted. 



1843. Klencke produced tuberculosis by intravenous injection 

 of tubercular giant cells. 



1865. Villemin demonstrated infectivity of tubercular matter by 

 inoculation of discharges; Cohnheim, Armanni, Burdon 

 Sanderson, Wilson Fox, and others showed that nothing 

 but tubercular matter could produce tuberculosis. 



1877. Living cells were found in tubercles, " micrococci " (Klebs, 

 Toussaint, Schiller). 



1882. Koch isolated and described the specific bacillus, and 

 obtained pure cultivations (1884). 



The Bacillus of Koch 



Biology. The B. tuberculosis of artificial culture is usually an 

 unbranched, slender, immotile rod, 1'5 to 4 /z long and '4 //, broad, 

 often slightly bent. In sputum and tissues the bacillus may appear 

 branched and in thread forms. The protoplasm of the bacillus 

 consists of fat and wax (26 per cent.),protamin (24 per cent.), nucleo- 

 proteid (23 per cent.), nucleic acid (8 per cent.), and the remainder 

 of mineral and proteinoid (chitin) substances. The protoplasm is 

 frequently vacuolated and irregularly segmented, and this becomes 

 particularly obvious after staining. As to staining, the bacillus is 

 acid-proof, and stains well with Ziehl-Neelsen or Gram. Klein and 

 Marmorek have shown that very young tubercle bacilli are not 

 resistant to acid and alcohol. Growth does not occur in the absence 

 of oxygen, is most favoured by a temperature varying from 29 C. 

 to 42 C., and is at all times slow on artificial media. In sputum 

 and in tissues it will be found that many of the bacilli are straight 

 with rounded ends; others are slightly curved. They are usually 

 solitary, but may occur in pairs, lying side by side or in small 

 masses. They are chiefly found in fresh tubercles, more sparingly 

 in older ones. Some lie within the giant cells ; others lie outside. 

 When stained, they appear to be composed of irregular cubical or 

 spherical granules within a faintly-stained sheath. In recent lesions 

 the protoplasm appears more homogeneous, and only takes on the 

 segmented or beaded character in old lesions, pus, or sputum. As 

 a rule, the capsule stains. There are no flagella. So far as is known, 



