526 BACTERIOLOGY. 



suspended bacteria, and, as a result, the liquid may contain few or 

 none. A loopful of the liquid, transplanted to bouillon, may there- 

 fore give no growth, although living- organisms may be present in the 

 tube. Constant results in this method can only be obtained by trans- 

 planting several larg-e drops by means of a drawn-out tube pipette. 



The Liborius tube is admirably adapted for testing by this 

 method. A small amount of dry Na 2 CO 3 on the point of a knife 

 (about 25 mg.) is placed in each tube. These are then sterilized in 

 the dry-heat sterilizer. 



To 20 c.c. of the bacterial suspension an equal volume of the 

 mercury solution is added observing the same precautions as under a. 

 At the end of 5, 10, 15, 30, 60 and 120 minutes about 2.5 c.c. of the mix- 

 ture are transferred to a Liborius tube which is connected at once 

 with a H2S generator. The gas should be passed for 1 or 2 minutes, 

 and the tube is then set aside for the mercury precipitate to subside. 

 When this has taken place 2-3 drops of the clear liquid are trans- 

 ferred by means of a sterile drawn-out pipette (p. 457) to a tube of 

 nutrient bouillon, which is eventually set aside in the incubator. 

 Obviously, the same pipette can be used in transferring- the several 

 portions of the original mixture to the Liborius tubes, but a separate 

 pipette must be used for each inoculation made from the latter. 



When the mixture undergoing examination contains a very 

 small amount of mercury (1-5000), or when gelatin or soap is present 

 the mercury sulphide will not precipitate but will remain in solution. 

 In such cases, it can be thrown out of solution by adding an equal vol- 

 ume of sterile saturated NaCl solution to the mixture in the Liborius 

 tube before the H 2 S is passed. 



Action of carbolic acid. A 10 per cent, solution of "carbolic acid is 

 first prepared, by the aid of gentle heat. 5 c.c. of the bacterial sus- 

 pension are placed in a sterile test-tube, Esmarch dish or small Erlen- 

 meyer flask, and an equal volume of the slightly warmed, perfectly 

 clear, 10 per cent, solution of carbolic acid is added. The liquid is at 

 once thoroug-hly mixed and cooled. At intervals of 1, 3, 5, 10, 15, and 

 30 minutes a loopful of the mixture is transferred to a tube of bouil- 

 lon which is labelled and eventually placed in the incubator. 



In the case of anthrax spores it will be well to inoculate bouillon 

 tubes with the mixture at the end of 1, 3, 6, 24, and 48 hours. The 

 liquid should be thoroug-hly mixed just before making each trans- 

 plantation. 



Action of lysol.The mixture of disinfectant and suspension is 

 made according to the directions just given. The tests are likewise 

 carried out in the same way. 



