ANTIBIOTIC SUBSTANCES 227 



philic chromogenic bacilli and certain micrococci {Micrococcus flavus) 

 are resistant to its action (263) ; however, it has no effect upon M. tu- 

 berculosis (834), Trypanosoma equiferdum^ and the influenza virus 

 (753). The purest preparation of penicillin so far available completely 

 inhibited (276) the growth of S. aureus in a dilution of between 

 1 : 24,000,000 and 1 130,000,000. Partial inhibition was obtained up to 

 1 : 1 60,000,000. Salmonella organisms were also sensitive. The antibac- 

 terial activity of penicillin is not interfered with by substances that in- 

 hibit sulfonamides, namely, bacterial extracts, pus fluids (7), tissue 

 autolysates, peptones, and ^-amino-benzoic acid. It is nontoxic in con- 

 centrations far greater than those required for therapeutic purposes 

 (163, 164). However, it is rapidly excreted through the kidneys and 

 frequent administration is essential in order to maintain a proper blood 

 concentration. 



In its biological properties, penicillin has been found, in general, to 

 resemble sulfonamide drugs, with certain significant differences (7) 

 which may be summarized as follows : 



The bacteriostatic power of penicillin against streptococci and staphylo- 

 cocci is greater than that of sulfonamides, even when the tests are 

 made under conditions optimum for the action of the latter. Satu- 

 rated solutions of sulfapyridine and sulfathiazole showed no com- 

 plete inhibition of bacteria on the assay plate, whereas peniciUin, even 

 in a dilution of 1 1500,000, gave considerable inhibition. 



The action of penicillin on streptococci and staphylococci, unlike that of 

 the sulfonamides, is influenced very little by the number of bacteria 

 to be inhibited. Bacterial multiplication could be completely pre- 

 vented by as low a concentration of penicillin as 1 : 1,000,000, even 

 if the inoculum contained several million bacterial cells. In the case 

 of smaller inocula, inhibition occurred in even higher dilutions. This 

 property of penicillin is believed to be of great importance in the 

 treatment of heavily infected wounds, on which the sulfonamide 

 drugs seem to have little beneficial action. 



The bacteriostatic power of penicillin against streptococci and staphylo- 

 cocci is not inhibited- to any extent by protein breakdown products or 

 by pus, which neutralize the bacteriostatic action of sulfonamide 

 drugs. The leukocytes remain active in any concentration of peni- 

 cillin usually employed in intravenous injection. 



