174 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



acid, a precipitate is produced, the filtrate containing virtually all the 

 activity. 



Streptothricin is completely adsorbed, at neutrality, on charcoal 

 (norit A), from which it can be removed by treatment for 8 to 12 hours 

 with dilute mineral acid or acid alcohol. The acid extract is neutralized 

 and concentrated in vacuo, at 50° C, just to dryness j the residue is ex- 

 tracted with absolute alcohol, filtered, evaporated, and taken up in 



TABLE 33. GROWTH OF STREPTOMYCES LAVENDULAE AND PRODUCTION 

 OF STREPTOTHRICIN ON TRYPTONE-STARCH MEDIUM 



water. It can also be precipitated from the neutralized solution with 

 ether. These preparations usually contain 40 to 50 per cent inorganic 

 matter and 2 to 3 per cent nitrogen, on an ash-free basis. Further con- 

 centration and reduction in ash content can be obtained by subsequent 

 treatments. On electrodialysis, the active substance moves to the cath- 

 ode at fH. 7.0. A highly active fraction has been isolated by chromato- 

 graphic adsorption on aluminum oxide. 



Streptothricin acts as a base, with an optimum at /)H 8.0. It is re- 

 pressed by dextrose and by acid salts. Bacteria subject to the action of 

 streptothricin show greatly enlarged cells, due to incomplete fission 

 (287, 1002). 



Another substance, designated as streptomycin (795), is similar in 



