STERILIZATION — ANTISEPSIS — FOpD PRESERVATION 8 1 



portion necessary to give the dilution wished. Mix thoroughly, 

 and allow this "action-flask" to stand as long as it is desired to 

 have the germicide in contact with the test-organism (action- 

 period). Transfer 0.5 c.c. from the action-flask to a flask contain- 

 ing 200 c.c. of a solution of some chemical capable of decomposing 

 the substance being tested with the formation of inert or insoluble 

 compounds. In this "inhibition-flask" the strength of the 

 solution should be such that molecular proportions of the chemical 

 are present in sufficient quantity to combine with all the germicide 

 carried over. The inhibition-flask is shaken for 30 seconds, and 

 I c.c. transferred from it to 100 c.c. of sterile water in another, the 

 "dilution-flask." After two minutes, three agar tubes are 

 inoculated with i r.c. each from the dilution-flask, plated, and 

 growth watched for. 



Control-experiments should be performed to determine that 

 the dilution of the test-culture is not too great when carried 

 through the three flasks. It likewise should be determined that 

 the inhibiting chemical has no effect on the bacteria. 



What the inhibiting chemical shall be must be determined 

 for each individual case. For salts of the heavy metals ammo- 

 nium sulphide answers well; for mercury salts, stannous chloride 

 may be used; for ' formaldehyde, ammonium hydrate; for car- 

 bolic acid, sodium sulphate. 



The testing of gaseous disinfectants, such as sulphur dioxide 

 and formaldehyde, must be conducted under conditions as nearly 

 parallel to actual practice as possible. The test-organisms may 

 be exposed on threads or cover-glasses, and acted upon by a known 

 volume strength of disinfectant for a known length of time. 

 Subsequent treatment of the organisms with a suitable inhibitor 

 is necessary when possible, and, should growth occur in the cul- 

 tures following, the test-organism should be recognized in order 

 that possible contamination by extraneous organisms may be 

 excluded. 



In determining the value of germicides for steriUzing ligatures, 

 the students can apply methods based on the foregoing principles. 



