ig6 MANUAL OF BACTERIOLOGY. 



cury. After exposing his test-organism to bichloride of mer- 

 cury, and before inoculating into bouillon to determine death 

 of the organism, he treated with a dilute ammonium sulphide 

 solution, thus effectually neutralizing any mercury-salt re- 

 maining. 



Sedgwick developed this method still further, and to him 

 we are indebted for demonstrating its accuracy and practica- 

 bihty. 



Sedgwick's Method. — To 15 c.c. of sterile water in a 60 c.c. 

 Erlenmeyer flask add 2 c.c. of a virulent culture of the test- 

 organism. Then add a solution of the substance under in- 

 vestigation in the proportion 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 containing 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 germicides 

 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 c.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 car- 

 ried through the three flasks. It likewise should be deter- 

 mined that the inhibiting chemical itself has no injurious effect 

 on the bacteria. 



The inhibiting chemical must be determined for each in- 

 dividual case. For salts of the heavy metals ammonium 

 sulphide answers well; for mercury salts, stannous chloride 



