Page:Popular Science Monthly Volume 17.djvu/850

830, benzoic acid and its salts, salicylic and metasalicylic acids, quinia, many aromatic substances, and alcohol, have long been known as such. Carbolic acid is the highest in repute among these poisons; and it is an interesting fact that Mr. E. Baumann has discovered this very substance among the products of the bacterian fermentation to which it is so fatal. Alcohol is another substance similarly associated. The discovery of the curious relations of these two substances gives a new light upon the cause of the spontaneous destruction of bacteria in strongly fermenting fluids, and encourages us to look for other substances having a similar origin and a like action. As evidence of the possession of such properties by any substance, we should require—

1. That substances favorable to the development of bacteria should remain free from them when the substance to be tested is added to them.

2. That active bacteria, when transplanted into a supporting mixture to which a substance supposed to be poisonous to them has been added, should cease to propagate themselves and die out. This may be called the aseptic test.

3. That, when the supposed poison is introduced into a solution swarming with bacteria, all living examples should be killed. This may be called the antiseptic test.

Various aromatic substances, the products of fermentation, were added to a mixture of water and chopped meat, at a temperature of 35° C They proved efficacious in preventing, suspending, or wholly stopping decomposition in the following order, according to the strength of their working:

(The working of scatol and hydrocinnamic acid could not be satisfactorily ascertained, on account of the difficulty of dissolving them in water.)

—killing transplanted organisms by poisoning the supporting fluid:

—wholly destroying all living bacteria:

Scatol, in the proportion of 0·5: 1,000 of the mixture, in twenty-four hours. Hydrocinnamic acid, in a proportion of 0·8: 1,000 of the mixture, in twenty-four hours.