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.
DISINFECTION STUDIES THE EFFECTS OF TEMPERATURE AND HYDROGEN ION CONCENTRATION UPON THE VIABILITY OF BACT. COLI AND BACT. TYPHOSUM IN WATER
Exposure to extremes of temperature and of hydrogen ion concentration produces an accelerated death rate of bacteria. These aTe typical conditions of ordinary disinfecting procedures. Temperatures and hydrogen ion concentrations in the zones between those which are favorable and those which are distinctly lethal may be expected to produce an adaptation in the organisms or a comparatively slow death rate, knowledge of which may reveal the conduct of bacteria under moderately unfavorable conditions in nature, and add to our understanding of certain phases of disinfection. The object of this study was to investigate the effects of variations in moderate temperature and moderate hydrogen ion concentrations upon the death rate in water and dilute buffer solutions. The experimental method imposed sub-lethal conditions upon the bacteria in contradistinction to the accelerated death induced by ordinary disinfecting procedures. It has been found in unbuffered media like distilled water or tap water that the death rates vary coincidently with apparently unimportant shifts in hydrogen ion concentration. When the pH factor is controlled by means of M/500 buffers, the death rates are stabilized so that comparisons become possible. The