The formation of gas in glucose bouillon varies considerably with the reaction of the medium. The largest amount of gas was formed when the broth was neutral or slightly alkaline. When the reaction of the broth was distinctly acid or distinctly alkaline the amount of gas was diminished. The gas which is formed in bouillon cultures consists chiefly of hydrogen and carbon dioxide. In order to collect a sufficient amount of the gas for analysis, two large fermentation tubes capable of holding 150 cubic centimeters each were constructed. These tubes were filled with pork-bouillon and inoculated with the bacillus. After 20 days at room temperature (20° to 25° C.) the gas was collected and the carbon dioxide and hydrogen determined, with the following result:
| Cubic centimeters. | |
| Total amount of gas collected | 37.7 |
| Carbon dioxide, by absorption with NaOH | 6.2 |
| Hydrogen, by difference | 31.5 |
This analysis gives an approximate gas formula of H/CO2= 5/1, which agrees with the gas formula as determined in the small fermentation tubes by Smith’s method.
In hams which had undergone spontaneous souring and in hams which had been artificially soured by inoculation, hydrogen-sulphid was often noted when the sour portions of the meat were tested with lead-acetate paper, but no distinct odor of the gas could be obtained. Hydrogen sulphid was also noted in egg-pork cultures of the bacillus.
ACID PRODUCTION.
In glucose-bouillon, butyric and lactic acids are formed and the reaction of the medium becomes distinctly acid. Butyric and lactic acids were also noted in the egg-pork cultures.
A series of Smith fermentation tubes containing 10 c. c. each of glucose-pork broth medium was inoculated with the bacillus and held at room temperature (20° to 25° C.). These cultures were titrated against [N/40]NaOH, with phenolphthalein as an indicator at intervals of two days up to nineteen days, and then at two-week intervals up to sixty-one days. Three of the cultures were titrated each time so as to give a fair average of the acidity of the cultures, and an uninoculated check tube was also titrated each time to see if there was any change in the reaction of the medium. The results of the titrations are shown in the following table:
Acidity determinations in glucose-pork broth cultures.
| Age of culture (days). | Culture A. | Culture B. | Culture C. | Average. | Medium. | Acidity of culture. |
|---|---|---|---|---|---|---|
| Per cent. | ||||||
| 2 | 0.038 | 0.030 | 0.040 | 0.036 | 0.009 | 0.027 |
| 4 | .105 | .100 | .102 | .102 | .009 | .093 |
| 6 | .106 | .110 | .109 | .108 | .009 | .099 |
| 8 | .124 | .115 | .117 | .119 | .009 | .110 |
| 10 | .128 | .130 | .126 | .128 | .009 | .119 |
| 12 | .129 | .120 | .129 | .126 | .009 | .117 |
| 19 | .126 | .125 | .125 | .125 | .009 | .116 |
| 33 | .125 | .123 | .125 | .124 | .009 | .115 |
| 47 | .122 | .120 | .121 | .121 | .009 | .112 |
| 61 | .121 | .116 | .119 | .118 | .009 | .109 |
From the above table it will be seen that the maximum acidity was reached at ten days, after which there was a gradual reduction in the acidity, due probably to the formation of ammonia compounds.