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by the most sensitive plate procurable, but when gathered together in multitudes, the magnitude of which even eight figures fail to express, these phosphorescent bacteria enable the dial of a watch to be easily read in the dark, whilst photographs of the face of a watch taken in such bacterial light have been so successful that the time at which the photograph was taken could be distinctly seen.

Of bacteria it may indeed truly be said, as has Maeterlinck of the labours of bees—“though it be here the infinitely little that without apparent hope adds itself to the infinitely little, though our eye with its limited vision look and see nothing, their work, halting neither by day nor by night, will advance with incredible quickness !”

Mention may perhaps appropriately be made here of the highly interesting fact discovered by Professor Percy Frankland, that ordinary bacteria which do not phosphoresce are capable of affecting a photographic film in absolute darkness, and can by this means produce a picture of themselves. If, however, a transparent piece of glass is placed between the bacteria and the film no photograph results, showing that glass interferes with their activity in this respect. The author points out that as this action upon the photographic film does not take place through glass, it is in all

probability due to the evolution by the bacteria of certain volatile chemical substances which either directly or indirectly enter into reaction with the sensitive film. Similar phenomena have been discovered in regard to many metals as well as organic substances, but this is the first observation which has been recorded of the action of living structures on sensitive films in the dark.

We have already referred to the important services which Pasteur has rendered by distinguishing between different varieties of yeast, and separating them out according to their functions and properties-pioneer work which has been followed up by and borne such splendid fruit in the hands of the renowned Danish investigator, Emil Christian Hansen of Copenhagen. This work of isolating out individual varieties of micro-organisms has been not only pursued with the energy familiar to all in the case of bacteria associated with disease, but has been pursued in various other, though perhaps less well known, directions.

A great deal of activity has lately been exhibited in so-called dairy bacteriology, and a long list has already been compiled of milk, cheese, and butter microbes; and agricultural authorities, even in this country, are slowly awakening to the fact that, in order to compete on modern lines with foreign dairy produce, dairy schools must

be established, where bacteriology is taught, and where instruction is given in the principles of scientific butter and cheese making.

But bacteria of the brewery and of the dairy are not the only useful germs which are to be found on the shelves of microbe museums. Wine and tobacco manufacturers on application may respectively obtain the bacterial means of transforming the crudest must into the costliest claret, and the coarsest tobacco into the most fragrant Havana. Already considerable progress has been made in the isolation of particular varieties of wine-yeast, whilst highly encouraging results have been obtained by Suchsland and others in the separation of various valuable tobacco-fermenting organisms. Agricultural authorities, again, owe a debt of gratitude to those distinguished investigators whose labours have discovered the art of imprisoning the micro-organisms which play such an important part in the fertilisation of the soil. Bacterial fertilisers are amongst the latest achievements which bacteriology has accomplished in this wonderful half-century, and the purchase of special varieties of bacteria to suit the requirements of particular kinds of leguminous plants is now fast becoming a mere everyday commercial transaction. But efforts for the amelioration of the conditions under which plant

life is carried on have not been confined to providing plants with suitable bacterial friends; vigorous and successful efforts have been made to remove from their entourage those bacterial enemies and undesirable parasites which have for so long played so important a part in the crop-returns of many an agriculturist.

For the identification and separation of the plant-parasites of various kinds we have largely to acknowledge our indebtedness to American investigators, and the encouragement and support which Dr. Erwin Smith, amongst others, has received from the Government of the United States in the prosecution of these researches indicates how great is the public importance attached to them. There are in America alone fifty experiment stations where plant diseases are studied, whilst at a number of the colleges and universities more or less attention is given to the subject. Some idea of the loss occasioned to agriculturists by these plant pests may be formed by a recent announcement that the Department of Agriculture in Queensland was prepared to offer a reward of £5,000 for the discovery of a means to eradicate the prickly-pear disease. Plant pathology has not yet had a distinct chair allotted to it in any of the great universities, but the subject is of such vast

industrial importance, that doubtless before long some seat of learning will do itself the honour to establish one, and so set the example.

A striking instance of the advantages of taking stock, so to speak, of the attributes of bacteria will occur to everyone in the revelation which has followed of their powers to solve one of the most knotty problems of the day—the efficient manipulation of those vast subterranean rivers of sewage which honeycomb every city of the world.

The purification which sewage underwent by passing it through the pores of the soil, or, in other words, by filtration, was recognised about the year 1870, soon after the Rivers Pollution Commissioners had begun to make their classical investigations on the land treatment of sewage; but although the rapid transformation of ammonia into nitrates which followed the passage of the sewage through a few feet of soil was noted, yet the mechanism of this nitrification process remained a mystery until 1877, when two French chemists-MM. Schloesing and Muentz-made the then astounding discovery that this change was dependent upon the vital energies of microorganisms.

The part played by bacteria in the purification of sewage thus became an established fact, and the later experiments have been devoted to study

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