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On the Toxic Action of Dilute Pure Sodium Chloride 

 Solutions on the Meningococcus. 

 By Cresswell Shearer, M.D., D.Sc., F.E.S., Military Hospital, Devonport. 

 (Received October 11, 1916.) 

 (Report to the Medical Research Committee.) 

 [Plate 15.] 



In experimenting during the past season with a large number of freshly 

 isolated strains of the meningococcus, it was noticed that almost all of these 

 were killed, when placed for a short time in dilute pure sodium chloride 

 solutions. This action of sodium chloride is most toxic to the meningo- 

 coccus when the concentration of the salt is not below - 85 per cent., and 

 not much above 09 per cent. XaCl. 



It was found that freshly isolated meningococci were more vulnerable to- 

 this action of XaCl, than old laboratory cultures. While old laboratory 

 cultures could sometimes resist the action of a pure - 85 per cent. XaCl for 

 three or four hours, freshly isolated strains seldom resisted its action for more 

 than 20 minutes. 



It seemed remarkable that XaCl should be toxic for the meningococcus in 

 just that concentration which it is accustomed to in the fluids of the body. 

 It is strange that this germ should be so sensitive to the toxic action of 

 sodium chloride, while at the same time it is able to resist for many hours the 

 action of distilled water. . 



To demonstrate the toxic action of a physiological saline solution on the 

 meningococcus, it is highly important to observe certain conditions in 

 performing the experiment. It is essential, in the first place, that the XaCl 

 used should be free from any impurity. In the second place, the meningococci 

 must be added to such a quantity of the saline solution that any traces of 

 salts brought over with them from the culture medium will have no 

 appreciable effect in antagonising the action of the XaCl. Thirdly, it is very 

 important that the saline is not unduly diluted below its proper toxic 

 strength by the addition of too large a quantity of the emulsion containing 

 the germs. In the fourth place, no agglutination of the germs into masses or 

 clumps in the saline must take place. The saline is unable to act on the 

 germs in the interior of these clumps, so that all are killed. Care must be 

 taken to shake up the germs in the saline thoroughly, and avoid all clumping 

 as much as possible. 



I have found from a large number of experiments that one or two drops 

 of an emulsion (of 5000 million meningococci to the cubic centimetre in 



