PENICILLIN 



95 



Fig 27. The Fleming culture and selected derivative strains. A, Stock, the Flem- 

 ing culture, NRRL 824. B, The Squibb strain derived from it, NRRL 1249. C, 

 NRRL 1249 B21, the strain most widely used for penicillin production in surface 

 culture. D, E, and F, Substrains of 1249.B21 showing varying patterns of growth 

 and a progressive reduction in spore production. (After Raper and Alexander, 

 Jour, of The Elisha Mitchell Scientific Society, 61, 1945.) 



