ANTAGONISTIC EFFECT OF SALTS 125 



From this it will be seen that the Cl-ion was the least, and the F-ion the most 

 toxic. 



One of the most extensive studies is that of Eisenberg (1919), who arranges 

 the anions in order of toxicity thus : SO4 <CS203 <^ Tartrate <^ H2PO2 <C M0O4 <C 

 CI < Br ; NO3 < SO3 < Fe(CN)6" " < Acetate < CIO3 < Citrate < HPO3 < 

 Oxalate < Formate < CNS < CIO4 < BrOg < I < H2PO4 < Benzoate < Nitro- 

 prusside < HASO4 < Cr04 < P2O7 < NO2 < F < BF4 < HF^ < BO3 < B4O7 < 

 Fe(CN)e" ' < Salicylate < HSe03 < IO3 <S208 < S^O, < TeOi < SbS4 < OSO4 < 

 IO4 < Cr^O^ < TeOj. 



The action of salts depends to a large extent on the medium in which they 

 are dissolved ; thus they are more active when dissolved in distilled water than 

 when dissolved in a medium containing protein. This is an observation that has 

 been made frequently (Behring 1890, Kronig and Paul 1897, Chick and Martin 

 1908). Probably it is due to the fact that many cations combine with proteins 

 to form an insoluble albuminate ; hence the concentration of free ions in the 

 medium is diminished. 



Another important observation is that different bacteria vary in susceptibility 

 to the same salt. v. Eisler (1909) found that B. subtilis was killed by N/10 LiCl. 

 whereas the El Tor vibrio was unharmed by N/5 LiCl. Eisenberg (1919) found 

 that B. anthracis possesses more than the average resistance to fluorides, iodates 

 and oxalates ; C. diphtherioe to telluratcs, tellurites, Ni and Cu ; Salm. typhi 

 to Sr salts ; the pneumococcus to ferricyanides and tellurites ; and V. cholerce 

 to chlorates and perchlorates. Certain organisms may be grouped together as 

 having a similar susceptibility to the action of salts ; thus. Staphylococcus pyogenes 

 and Staphylococcus candicans ; C. diphtherioe and the diphtheroid bacilli ; Salm. 

 typhi and Bact. coli ; Chromo. prodigiosum and Chromo. kielense are grouped in 

 pairs, each member of the pair exhibiting a similar susceptibiUty to different salts. 



As well as this relationship, however, there is a difference in resistance exhibited 

 between members of the Gram-positive and the Gram-negative group of organisms. 

 Eisenberg found that many salts are more toxic to the Gram-positive than to the 

 Gram-negative bacteria. This holds not merely for particular salts, but for their 

 constituent anions and cations. On the other hand, some salts, such as potassium 

 tellurite (Fleming 1932, Fleming and Young 1940) and sodium azide (Snyder and 

 Lichstein 1940, Mallmann et al. 1941), are more toxic to Gram-negative than to 

 Gram-positive bacteria. This property is now made use of in the preparation of 

 selective media. 



The diflference in susceptibility to sodium chloride has been suggested by Schoop (1935) 

 as a criterion for bacterial classification. He divides bacteria into three qlasses : (1) those 

 that grow in ordinary media, but not in media containing 10 per cent. NaCl^non-halophiles ; 

 (2) those that grow in both media — facultative halophiles ; (3) those that grow only in 

 media containing 10 per cent. NaCl — obhgatory halophiles. The last group of organisms 

 are found mainly in sea water, and in sand and mud adjacent to the sea. 



Antagonistic Effect of Salts.^Hitherto we have been considering the effect on 

 bacteria of solutions containing one salt ; we must now examine the effect of 

 solutions containing more than one salt. 



Flexner (1907) found that an 0-85 per cent, solution of NaCl caused rapid 

 disintegration of the meningococcus ; but that when a calcium salt was added 

 to the solution, this disintegration no longer occurred. The conclusion he drew 

 was that NaCl by itself is toxic to the meningococcus, but that its toxic action 



