The microscopic germ is every day pushing more to the front and threatening to elbow the mere molecule out of the field. Even familiar chemical reactions will not come off if nothing else but the chemicals concerned is present; there has to be something to start the reaction, something electrical or who knows what. So we are told. Any day we may expect to hear that the electrons are alive; at any rate they are pretty lively and capable for "dead" things. Bacteria are not all deadly or even maleficent. There are bacteria that are good for us, necessary for our existence. The human body can be described as made up of minute organisms. Disease means that the destructive ones have prevailed over the constructive; but when there is a proper balance of the two sorts we are healthy. And now we learn that some of the beneficent bacteria shine--emit light--a sure token of their saintly character! But they do not merely absorb it and give it out again like some chemicals and phosphorescent bodies; they create their own light. "_Fiat Lux_," they say, _et lux fit_. This light, too, is without heat, wherefore it is the most economical light possible. When _we_ create light we create with it enough heat to run a hell, and all this represents waste. The most efficient electric filament, it is said, gives only 5% of the energy in the form of light. The luminous bacteria must have a nutritive substance and oxygen. They abound most in sea-water, and on the Pacific Coast the sea at certain seasons is a magnificent spectacle at night, each wave shining with a soft bright light of undefinable colors. But they can be experimented with in the laboratory. _Photobacterium phosphorescens_ is obtained from the herring, duly fed and bottled, and can be used to read by. A scientific magazine shows a photograph of a picture of Lord Lister most appropriately illuminated by bacteria which are contained in glass tubes near the picture. Light has been regarded mainly as a means of vision; but it is evidently more than this. In ancient science it is spoken of as one of the creative powers. In physics we recognize it as among the active transforming forces. We can regard it either as a form of energy or as a form of matter--these amounting to little more than alternative points of view. Behind the various phenomena classed as "light" lies their ultra-physical _cause_--the _being_, the _thing-in-itself_. When we speak of light as illuminating the mind or emanating from the source of inspiration, we are commonly held to be employing a figure of speech, a metaphor. But we might as well turn the matter around and regard the scientific use of the word light as a metaphor.