Action of Sodium Chloride Solutions on the Meningococcus. 441 



distilled water) is the proper quantity of emulsion to be added to 2 c.e. of 

 0'85 per cent, saline to effectively demonstrate the toxic action of pure NaCl 

 on the meningococcus. 



The toxic action of a - 85 per cent. NaCl solution on the meningococcus 

 can be readily antagonised and rendered harmless by the addition of a very 

 small trace of some bivalent salt, such as CaCLj, with or without the addition 

 of a small quantity of KC1. This is clearly shown by the following experi- 

 ment, which has been repeated many times. 



A twenty-four-hour culture of a recently isolated strain of meningococcus 

 "Lake" was emulsified in distilled' water ; a fairly thick emulsion being 

 prepared (about 5000 million cocci to the cubic centimetre). Into four 

 sterile test-tubes, capable of being placed in a centrifuge, the following 

 solutions, with 25 cu. mm. of the meningococcus emulsion, were placed as 

 follows :— 



1. 2 c.c. sterile - 85 per cent. NaCl. 



2. 2 c.e. „ 0-85 „ NaCl + 0'004 c.c. M/l CaCl 2 . 



3. 2 c.c. „ 0"85 „ NaCl + 0-004 c.c. M/l CaCl 2 + 0-01 c.c. M/l KC1. 



4. 2 c.c. „ distilled water. 



Each tube was then thoroughly shaken to ensure thorough mixing of the 

 solutions and the emulsion of cocci. They were put in the incubator at 

 37° C. for an hour and a quarter. They were then taken out and centrifuged 

 hard for 15 minutes, and the deposit in each tube planted out separately, in 

 sterile fashion, on a chocolate plate.* Fig. 1 shows the growth obtained on 

 this plate after incubation for 24 hours at 37° C. 



An examination of fig. 1 shows that the meningococcus emulsion placed in 

 the pure 0'85 per cent. NaCl, that is the deposit from the tube 1, has failed 

 to grow, and that this quarter of the plate (marked N.S.), planted out with 

 this deposit, is quite free of colonies. The cocci have been killed by the 

 saline. In the opposite quadrant of the plate to this (marked II on the 

 margin of the plate), which has received a similar quantity of emulsion 

 in - 85 per cent. NaCl, with the addition of a trace of CaCl2, a thick heavy 

 growth of the meningococcus has taken place, covering the entire surface of 

 this quarter of the plate. The CaCl 2 here has completely antagonised the 

 toxic action of the NaCl. In quadrant III, where the saline has received 

 the same quantity of CaCl 2 as II, but also a little KC1, growth is still 

 thicker (not very well shown in the photograph). In IV, where the germ 

 was simply allowed to stand for an hour and a quarter in distilled water, 

 growth is good, and the colonies cover closely the entire surface of this 

 quarter of the plate. 



* Crowe's " chocolate " or blood-trypagar-glucose medium. See 1 Lancet,' November 21, 

 1915. 



