Journal of Agricultural Research 



Vol. XX, No. a 



EXPERIMENTS WITH STAPHYLOCOCCUS AUREUS, BACILLUS PYOCY- 

 ANEUS, AND B. TYPHOSUS AS TEST ORGANISMS 



The cultures used in this series of experiments were stock cultures 

 which had been carried along in this laboratory for some time. They 

 had been previously examined in connection with other work and had 

 been found true to type. The cultures of Staphylococcus aureus and 

 Bacillus pyocyaneus were originally isolated from wounds and when re- 

 ceived in this laboratory were virulent for guinea pigs and rabbits. 



The first three experiments of this series were made with chloramin 

 T only. The results are shown in Tables I and II. 



Experiment i. — This was a preliminary experiment to test the value 

 of chloramin T against Staphylococcus aureus and Bacillus typhosus. The 

 technic was as follows: One-tenth cc. of 24-hour bouillon culture was 

 mixed with 25 cc. of blood serum. 1 Then 2.5 cc. of this mixture were 

 mixed with 2.5 cc. of a dilution of chloramin T. After exposures of one 

 hour and two hours, respectively, subcultures were made with a 3-mm. 

 platinum loop into tubes of standard bouillon containing enough sodium 

 thiosulphate to neutralize the disinfectant carried over. 



The number of organisms present in the test mixtures were calculated 

 to be 1,340,000 per centimeter for Staphylococcus aureus and 800,000 per 

 centimeter for Bacillus typhosus. Dilutions given in the table are, of 

 course, final dilutions, and the dilutions actually made up to begin with 

 were naturally just twice as concentrated. The results are given in 

 Table I. 



Table I. — Germicidal efficiency of chloramin T against Staphylococcus aureus and 

 Bacillus typhosus, mixed with blood serum, using equal amounts of disinfectant and 

 of serum plus culture ° 



EXPERIMENT I 



Concentration of chloramin T. 



Staph, aureus. 



B. typhosus. 



Exposed Exposed i Exposed 

 1 hour. 2 hours. i hour. 



Exposed 

 2 hours. 



°+ Signifies growth; — , no growth. 



Experiments 2 and 3. — The technic used in these experiments was 

 as follows : Each disinfectant dilution was mixed with an equal quantity 

 of blood serum (2.5 cc. each of disinfectant dilution and serum), and to 

 this mixture 2 drops of a 24-hour bouillon culture were added. The 

 mixture was then vigorously shaken, and at intervals of 15 minutes, 

 1 hour, and 2 hours subcultures were made with a 3-mm. platinum loop 



1 Horse-blood serum was used In all experiments where blood serum is mentioned. 



