ANTIBACTERIAL ACTION 



239 



the latter merely decreasing the rate of multiplication and the former 

 actually bringing about a decrease in the number of organisms present. 

 This is shown in Figure 22. The rates of activity of penicillin, grami- 

 cidin, and tyrocidine are compared in Table 25 (p- 220). The bac- 

 tericidal action of penicillin is greatly influenced by the age of the cul- 

 ture, young cultures being readily killed whereas older cultures are 

 only little affected. No penicillin is absorbed or destroyed by the bac- 

 teria. 



Penicillin is not very stable (760). It is sensitive to reaction and 

 temperature changes. The effect of reaction upon the stability of peni- 

 cillin is shown in Figure 23. The thermostability of pyrogens and their 

 removal from penicillin preparations are also important (996). 



Para-amino-benzoic acid and sulfapyridine were found to have a 

 synergistic effect on penicillin. A solution of sodium penicillin with 

 1,200 units per milliliter gave 100 B. subtilis units in a synthetic casein 



2 4 6 8 10 



REACTION (pHj 



2 4 6 8 10 



REACTION (pH) 



Figure 23. Inactivating effect of reaction upon penicillin. From Foster and 

 Wilker (283). 



