Page:Popular Science Monthly Volume 15.djvu/763

 showed during this time no disposition to germinate. They were not killed, however, they only slept; for, on the substitution of common air for the etherized air with which they had been surrounded, germination at once set in and proceeded with activity.

Experiments were also made on that function of plants by which they absorb carbonic acid and exhale oxygen, and which, as we have already seen, is carried on through the agency of the green protoplasm or chlorophyl, under the influence of light—a function which is commonly, but erroneously, called the respiration of plants.

Aquatic plants afford the most convenient subjects for such experiments. If one of these be placed in a jar of water holding ether or chloroform in solution, and a bell-glass be placed over the submerged plant, we shall find that the plant no longer absorbs carbonic acid or emits oxygen. It remains, however, quite green and healthy. In order to awaken the plant, it is only necessary to place it in non-etherized water, when it will begin once more to absorb carbonic acid, and exhale oxygen under the influence of sunlight.

The same great physiologist has also investigated the action of anaesthetics on fermentation. It is well known that alcoholic fermentation is due to the presence of a minute fungus, the yeast-fungus, the living protoplasm of whose cells has the property of separating solutions of sugar into alcohol, which remains in the liquid, and carbonic acid, which escapes into the air.

Now, if the yeast-plant be placed along with sugar in etherized water, it will no longer act as a ferment. It is anæsthesiated, and can not respond to the stimulus which, under ordinary circumstances, it would find in the presence of the sugar. If, now, it be placed on a filter, and the ether washed completely away, it will, on restoration to a saccharine liquid, soon resume its duty of separating the sugar into alcohol and carbonic acid.

Claude Bernard has further palled attention to a very significant fact which is observable in this experiment. While the proper alcoholic fermentation is entirely arrested by the etherization of the yeast-plant, there still goes on in the saccharine solution a curious chemical change, the cane-sugar of the solution being converted into grape-sugar, a substance identical in its chemical composition with the cane-sugar, but different in its molecular constitution. Now, it is well known from the researches of Berthelot that this conversion of cane-sugar into grape-sugar is due to a peculiar inversive ferment, which, while it accompanies the living yeast-plant, is itself soluble and destitute of life. Indeed, it has been shown that, in its natural conditions, the yeast-fungus is unable of itself to assimilate cane-sugar, and that, in order that this may be brought into a state fitted for the nutrition of the fungus, it must be first digested and converted into grape-sugar, exactly as happens in our own digestive organs. To quote Claude Bernard's graphic account: "The fungus ferment has thus beside it