STUDIES ON SALT ACTION
Ih an earlier paper (Falk, 1923) our present state of knowledge in regard to the physiological influence of mineral salts upon bacteria has been somewhat comprehensively reviewed. The experiments here reported were designed to determine with some exactness the effect upon bacterial viability of sodium and calcium chlorides, alone and in combination. Our work has extended over a long period, the first preliminary communications (Winslow and Falk, 1918) having been made over four years ago. The early experiments at times yielded conflicting results and it was only by a careful study of the hydrogen ion factor (Falk, 1920) that we succeeded in explaining these inconsistencies along the lines since so well worked out for problems of bacterial growth by Holm and Sherman (1921) and Sherman and Holm (1922). The study presented here deals with the viability of Bactenium coli in distilled water, in various concentrations of NaCl, and in various concentrations of CaCl2 with varying hydrogen ion concentrations for each solution; while a following paper (IJX) deals with viability in various mixtures of the two salts mentioned above.
The Bacteriostatic Activity of Cerium, Lanthanum, and Thallium
The salts of cerium, lanthanum, and thallium have long been known to possess bacteriostatic properties in low concentrations, but there is little infornation in the literature concerning the variability of their toxicity toward different species of microorganisms. A report of the concentrations of the salts limiting development of various types of bacteria may have importance in relation to their possible use as bacteriostatic or bactericidal agents. Bokorny (1894) found cerium compounds relatively much more toxic for bacteria than for algae. Hebert (1907) reported that cerium and lanthanum sulfates in concentrations of 5 to 10 grams per liter showed little toxicity toward Aspergillus niger and yeast. Sartory and Bailly (1922) reported that 0.2 per cent lanthanum sulfate depressed the growth of Aspergillusfumigatus in Raulin's solution and practically inhibited spore formation. Frouin (1912) observed that 0.005 grams of lanthanum sulfate per 100 ml of medium stimulated the growth of the tubercle bacillus but that higher concentrations were toxic. Frouin and Roudski (1914) studied the toxicity of lanthanum and thorium for the cholera and dysentery organisms. Other investigators who reported bacteriostatic or lethal effects of salts of the rare earth group include Drossback (1897), Brooks (1921), Grenet and Drouin (1927), Zirpolo (1924), Frouin (1920), Simonini (1914), Doerr (1920), Eisenberg (1918), and Hotchkiss (1923). A general review of the earlier literature on this subject is found in Buchanan and Fulmer (1930). McKenzie (1941) employed thallium acetate in a medium recommended for the enrichment of the streptococci causing mastitis. The effect of cerium on enzyme activity was reported by Gould (1936). Olszewski (1932) observed no significant reduction in the bacteria of river water when 1 ppm of cerous or ceric chloride or ceric sulfate was employed. Richards (1932) reported thallium to be a growth stimu.lant for yeast. The present paper reports a further investigation of the bacteriostatic activity of the salts of cerium, lanthanum, and thallium.
Studies on salt action. IV. The mutual influence of acidity and salt concentration upon bacteria
Four years ago 1 we presented certain preliminary results of studies on the toxic influence of calcium and sodium salts upon Bact. communis; and two years ago one of us 2 called attention to the possible influence upon such salt effects of the reaction of the solution. In our earlier experiments the reaction of the distilled water and salt solutions to which the bacteria were exposed was not controlled though the media were in general alkaline (PH 8.0-9.0). Under these conditions we obtained the following results with various concentrations of NaCl and CaCl2. Later experiments, in which the hydrogen-ion content was maintained at various desired levels by repeated readjustment, gave quite different results, as indicated below. These results (which are all based on averages of a sufficient number of tests to eliminate chance variations) were at first highly puzzling. In the unadjusted alkaline solution 5.0 isotonic NaCl was moderately toxic and I .o isotonic CaCl2 highly toxic. At adjusted PH values on the other hand 5.0 isotonic NaCl2 remained at practically all reactions slightly more toxic than water but 1.o isotonic CaC12 entirely lost its toxicity and became actually stimulating, at least at PH values between 5.0 and 7.0. It appeared therefore that neither 5.0 isotonic NaCl nor 1.0isotonic CaC12 is in itself toxic at adjusted PHvalues between 6.0 and 7.0; and that at an adjusted PH much over 7.0 both salts, as well as distilled water, are definitely toxic. What conditions could have existed in the earlier work, at uncontrolled PH, to make 1.0 isotonic CaCl2 toxic and 5.0 isotonic NaCl nearly non-toxic? The key to this riddle, first suggested by the experiments reported here two years ago, has been found in the influence of salt content upon the power of a bacterial suspension to regulate its reaction.