TOXICITY OF SODIUM, POTASSIUM AND LITHIUM 313 



though the points representing radial growth in the graph do not 

 lie exactly on the smooth curve they are sufficiently close to it to 

 show fairly accurately the relation between decreasing growth 

 and increasing sodium chloride concentration. It is clear that 

 this relation is not a straight line but one showing a decreasing 

 ratio (decrease in growth /salt concentration) with increase in 

 sodium chloride. As the ratio (salt ion/salt concentration) also 

 decreases with increasing concentration of sodium chloride, the 

 data may have some weight on the hypothesis that the ions are 

 more active than the salt molecules. This idea should be held 

 with reservations, however, until we can secure data on the other 

 salts by the alternative methods discussed above and learn the 

 specific effects of the various cations, anions and molecules. 



CONCLUSION 



1. Endothia parasitica (Murr.) Anders grows excellently on malt 

 extract, corn meal extract and bean decoction media regulated 

 between pH = 5 and pH = 7, and buffered with M/50 K 2 HP0 4 

 and M/50 acetic acid to prevent the marked changes in pH pro- 

 duced in passing from the neutralization of the first hydrogen ion 

 to the second of phosphoric acid. 



2. In such a buffered malt extract medium regulated at about 

 pH = 5, the addition of sodium chloride up to 0.63 N or 3.65 

 per cent causes a gradual -decrease in the rate of growth to about 

 25 per cent of the normal value. This salt is therefore only 

 mildly toxic, contrary to the statements of Wolesky. 



3. The form of the growth curve suggests the possibility that 

 the salt ions are more toxic than the salt molecules, but this con- 

 clusion should be considered tentative until extensive work on this 

 and other salts can give the values for the toxicities of the cations, 

 anions and nonionized molecules of such electrolytes. 



THE JOURNAL OF BACTERIOLOGT, VOL. V, NO. 3 



