528 BACTERIOLOGY. 



The student should test tfte antiseptic action of several chem- 

 icals, according- to the following directions, on one of the bacteria 

 employed in the disinfection experiments. 



Antiseptic action of mercuric chloride. A bacterial suspension is 

 made by adding- a few drops of a fresh bouillon culture of the germ 

 to about 200 c.c. of sterile bouillon. The 1: 500 mercuric chloride solu- 

 tion is also used. 4 larg-e sterile tubes are numbered consecutively, 

 and equipped as follows: 



No. 11 c.c. of the Hg-Cl 2 + 9 c.c. of the suspension = 1: 5,000. 

 No. 20.5 c.c. of the Hg-Cl a + 9.5 c.c. of the suspension = 1: 10,000. 

 No. 3-0.25 c.c. of the HgGla + 9.75 c.c. of the suspension = 1: 20,000. 

 No. 40.1 c.c. of the Hg-Cl 2 -f 9.9 c.c. of the suspension = 1:50,000. 



The tubes are then placed in the incubator and examined at the 

 end of 24 hours. From the cultures that show no growth, or at most 

 a very faint cloudiness, a few drops should be transplanted to sterile 

 bouillon tubes. The two sets should be returned to the incubator and 

 examined on the following day. Hanging-drop preparations of the 

 two sets should be made. Involution forms may be expected. The re- 

 sults should be tabulated. 



Antiseptic action of carbolic acid. An aqueous 1 per cent, solution of 

 phenol is placed in a stoppered flask or bottle and steamed for a few 

 minutes. The same bacterial suspension is used as above. 5 sterile 

 tubes are numbered and equipped as follows: 



No. 1 2 c.c. of the phenol + 8 c.c. of the suspension = 1: 500. 

 No. 2 1 c.c. of the phenol + 9 c.c. of the suspension = 1: 1,000. 

 No. 3 0.5 c.c. of the phenol -+- 9?5 c.c. of the suspension = 1:2,000. 

 No. 40.25 c.c. of the phenol + 9.75 c.c. of the suspension = 1: 4,000. 

 No. 50.1 c.c. of the phenol + 9.9 c.c. of the suspension = 1: 10,000. 



The tubes are then placed in the incubator and examined as in 

 the preceding experiment. 



Antiseptic action of formaldehyde. 2.5 c.c. of the commercial 40 per 

 cent, solution of formaldehyde are diluted to 100 c.c. with sterile 

 water ( = 1 per cent.). A series of 5 dilutions is then made employing- 

 the same quantities as in the above experiments. 



Antiseptic action of sodium benzoate. An aqueous 1 per cent, solu- 

 tion of this salt is sterilized by exposure to steam. The 5 dilutions 

 are prepared and tested in exactly the same manner as in the case of 

 carbolic acid. 



