Sodium Chloride Solutions on the Meningococcus. 443 



the plate inoculated with a similar quantity of the same emulsion of the 

 meningococcus, which had been exposed to the action of a 1*5 per cent. NaCl 

 solution. Thus, as Loeb has found, when the concentration of the NaCl 

 solution increases the toxic action diminishes. 



I should like to draw attention, finally, to an experiment made to deter- 

 mine the length of time the meningococcus may remain alive in pure 

 distilled water, as compared with the time it can remain alive in a 0'85 per 

 cent. NaCl solution. 



Into 4 c.c. of distilled water and 4 c.c. of 085 per cent. NaCl solution 

 respectively, 25 cu. mm. of a meningococcus emulsion was placed. The two 

 solutions were incubated for 24 hours at 37° C, centrif uged down for an hour, 

 and planted out separately on a chocolate plate. In fig. 3 is shown the 

 resulting growth on this plate after 24 hours' incubation at 37° C. The 

 saline, as usual, has killed the germs, while a considerable number of those 

 that have been exposed to the action of the distilled water for 24 hours have 

 survived, and have given rise to an extensive growth. This experiment 

 clearly demonstrates the power of the meningococcus to resist the hypo- 

 tonic action of distilled water for many hours. 



This experiment has been repeated with a large number of different strains 

 of the meningococcus, and it was found that considerable difference in this 

 power of withstanding the action of distilled water was possessed by each 

 strain. It was the exception, however, to find a strain which did not survive 

 the exposure to the action of distilled water at 37° C. for three hours. 



DESCRIPTION OF PLATE 15. 



Fig. 1. — Photograph of the growth obtained on a plate of Crowe's chocolate medium 

 after 24 hours' incubation at 37° C, showing the toxic action of a pure 0"85 per cent. 

 NaCl solution on the meningococcus and the antagonistic action of a trace of CaCl 2 . 



I. Portion of plate planted out with emulsion of the meningococcus in 0'85 per cent. 

 NaCl solution. No growth whatever has taken place, all organisms being killed. 



II. Portion of plate planted out with a similar quantity of emulsion in 0"85 per cent. 

 NaCl + a trace of CaCl 2 ; here the CaCl 2 has antagonised the toxic action of the 

 NaCl, with a resulting thick growth of the meningococcus. III. Portion of plate 

 planted out with a similar quantity of emulsion in 0'85 per cent. NaCl + CaCl 2 + KCl, 

 with a resulting thick heavy growth, more than in II. IV. Portion of plate planted 

 out with a similar quantity of meningococcus emulsion which had been allowed to 

 stand for l£ hours in distilled water ; good growth. 



Fig. 2. — Showing the toxic action of 0'85 NaCl solution on the meningococcus, in 



distinction to the relatively harmless action of a 1*5 per cent, solution of the same 



salt. N. Normal saline solution. 

 Fig. 3. — Showing the action of distilled water in failing to kill the meningococcus after 



24 hours. D. Distilled water portion. N.S. Saline portion of the plate ; all germs 



killed. 



