TUBERCULOSIS. 77 



products of more than one bacterium constitute the causal factors in 

 this form of poisoning. 



Koch's tuberculin, with which he hoped to cure the disease, is the 

 crude poison formed by his bacillus and is known as tuberculin. 

 The methods of preparing this substance have varied somewhat and 

 we will mention some of them. Koch prepared tuberculin in the 

 following manner : Meat infusion containing one per cent, of pepton 

 and from four to six per cent, of glycerin is placed in sterilized 

 flasks with broad bottoms. The flasks are only partially filled in 

 order that the surface of the fluid should be as great as possible. 

 A small mass of a growth of tubercle bacilli is taken from a culture 

 on glycerin agar or blood serum, and floated on the surface of the 

 meat infusion in the flask, which is then placed in an incubator at 

 37°. The bacilli grow abundantly on the surface of the meat infu- 

 sion, forming a thick, yellowish-white layer. After about six weeks, 

 growth stops, the bacterial layer begins to break into pieces and these 

 fall to the bottom of the flask. The culture is now evaporated to 

 one-tenth its volume on the water-bath. The concentration increases 

 the per cent, of glycerin to from forty to fifty, and this ingredient 

 prevents the growth of extraneous bacteria and renders the fluid per- 

 manent for an indefinite time. After filtration through porcelain, 

 this fluid constitutes the crude tuberculin of Koch. It will be seen 

 that it must contain, in addition to the water and glycerin, any other 

 soluble, unchanged constituent of the original meat infusion, any 

 split products, if there be such, arising from the cleavage action of 

 the bacilli on the components of the culture medium, and all soluble 

 constituents of the bacterial cells. The toxin in this impure form 

 is not destroyed by the temperature of the water-bath. Ultimate 

 analyses of the crude tuberculin have been made, but it must be 

 evident from what has just been said concerning the complexity of 

 its composition that such determinations are without value. It does 

 not contain any ptomain or other basic body. 



Bujwid obtained tuberculin by extracting the growths of the 

 bacillus on glycerin agar tubes, heating to 100° for ten minutes, 

 filtering through porcelain and concentrating at a low temperature. 

 As thus prepared, the fluid resembles very much the preparation 

 already described. 



Tuberculin may also be obtained from bacilli grown on potatoes. 

 The freshly cut surfaces of the sterilized potatoes are washed with a 

 1 per cent, sterilized solution of sodium bicarbonate, then mois- 

 tened with sterilized water containing five or six per cent, of glyce- 

 rin. On potatoes thus prepared the bacillus grows abundantly at 

 a temperature of 37°. After further development has ceased, the 

 growths are extracted with water or water and glycerin. 



In 1897 Koch' reported his attempts to improve the preparation 

 ^DeviacheTned. Woehenschr^, 1897, 209. 



