76 BIOLOGY OF PNEUMOCOCCUS 



rially amplified our knowledge of this phenomenon of peroxide pro- 

 duction by bacteria. Avery and Morgan 52 noted the early appear- 

 ance of peroxide in cultures of pneumococci and of non-hemolytic 

 streptococci, with a somewhat retarded development in cultures of 

 some but not all strains of S. haemolyticus and S. mucosus. Per- 

 oxide was not detected at any time during the growth of two 

 strains of Staphylococcus aureus. The factors influencing peroxide 

 formation were free access of air, and the absence of a catalase, 

 peroxidase, or other catalyst capable of decomposing H 2 2 . Under 

 favorable conditions peroxide production continued during the 

 logarithmic phase of growth and persisted for at least six to twelve 

 days. According to Avery and Morgan the aerobic growth of 

 anaerobic bacteria in broth containing sterile, unheated plant tis- 

 sue may be related to the action of oxidizing-reducing systems of 

 plant tissue in the destruction of toxic peroxides formed during 

 bacterial growth. These assumptions were supported by subse- 

 quent experiments by Avery and Neill, 55 in which it was found that 

 anaerobically grown pneumococci rapidly form peroxide on ex- 

 posure to molecular oxygen. The peroxide-forming properties of 

 pneumococci varied with different strains and with the age of the 

 cells, and were active under conditions of reaction and temperature 

 that did not permit active cell growth and multiplication — a range 

 of pH 5.0 to 8.5 — and at lower temperatures than those that fa- 

 vor growth. 



Avery and Neill, 56 employing sterile, filtered extracts prepared 

 by freezing and thawing pneumococcal cells or by dissolving them 

 in bile, proved that the peroxide-forming ability of Pneumococcus 

 is a function not dependent upon the presence of living, intact 

 cells. Sterile extracts of unwashed pneumococci promptly formed 

 peroxide on exposure to air; its formation was almost as active in 

 extracts aerated at 2° as in those exposed to air at room tempera- 

 ture. The optimal zone was on the alkaline side of pH 6.0, but 

 peroxide was detectable in the range pH 5.0 to 9.0. The peroxide- 



