Abstract
It is well known that the rate of bacterial autolysis as measured either by morphological disintegration or by chemical determination of the accumulating split-products, varies widely among the pathogens. No mention could be found, however, of this process being accelerated by an aldehyde. Certain strains of the gram-negative diplococci (thrice washed in saline) have been found to become acid in suspensions containing appropriate concentrations of formaldehyde. While most of these observations were made on bacterial suspensions equivalent to 0.25% dry weight of organisms, the reaction was found to be roughly proportional to the concentration of bacterial material. The acidification was measured by the frequency with which small additions of N/10 NaOH were required to bring the reaction of the suspensions back to pH 7.2. It was most rapid in concentrations of 0.7-2% formaldehyde, was much slower (about one-eighth the maximum) in 4% and failed to occur in 8% formaldehyde. It was more rapid at 37°C. than at room temperature.
No acidification took place when, before adding formaldehyde, the suspension was boiled for 1 minute, heated to 75°C. for 5 minutes, or 60°C. for 20 minutes. A temperature of 50°C. for several days did not inhibit the action noticeably. The presence of 10% alcohol reduced the action and 20% alcohol prevented it altogether. Heavy metal showed an inhibitory property, e. g., 0.1 mg. of silver nitrate per 10 cc. inactivated the mixture. 0.001 mg. potassium cyanide per cc. of suspension prevented the reaction.
Suspensions which had been rendered alkaline to phenolphthalein for a few hours failed to become acid. A suspension started at pH 7.2, to which no alkali was added during 7 days at 37°C., developed an acidity of pH 3.2.
Accompanying the acidification of the formolized suspensions is an increase in the non-protein nitrogen as compared with the control suspensions.
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