BACTERIA—PLEASANT AND UNPLEASANT.

Otago Daily Times, Issue 18446, 6 January 1922, Page 9

BACTERIA—PLEASANT AND UNPLEASANT.

The romance of bacteria is not the least interesting part of the vast system of dis coveriea which we call modern science. It •was probably in 1683 that a few larger specimens of that wonderful population first dawned upon a human eye. Some of them are about l-250th of an inch in diameter—they run down to 1-25,000 th of an inch, or less—and the first lens of any power would glimpse them. But until the middle' of the nineteenth century they remained vague and ghostly forms, on the very edge of the range of the miscroscope, known only to a few enthusiasts in every country. A Million a Drop.— It was about 1870 when the serious study of bacteria began. In this short period of half a century we have traced, classified, and studied a living population beyond the dreams of any earner naturalist. In very choice specimens of sewage water there may be as many as 20 million “microbes” to the cubic centimetre—say, a million to each drop. In some of our laboratory cultures they may be far denser than this. These are “congested areas,” but, as everybody knows, they teem over a very large part of the earth. They float in the air, they fill the soil, they swarm in most fluids; and they are beyond the powof counting in our ditches and ponds aid sewers and refuse heaps, Analysing the Ice Cream. — The general public is apt to run now to the opposite extreme, and think that the earth was a brighter place to live in before we knew anything at all about these fearful hordes. What is life, in the summer, without an ice now and again? Yet this horrible person, the bacteriologist, comes along and tells you, cheerfully, that there are few things which bacteria love better than ice cream. Some years ago—things are a little better to-day, we hasten to say—one of them analysed specimens of London ice cream. With unconscious humour he pronounced it “not inferior to London sewage”; and London sewage has a good average of five million bacteria to the cubic centimetre. The pitblic shuddcringly wonders whether it is actually introducing these bacteria into its sacred anatomy. Well, the truth is that each of ns has billions of bacteria inside him, and they are so useful that it is doubtful if we could get on without them. There are six different tribes of them in the mouth, and those we could very well do without. There are other tribes in the nose—you shoot out a whole village or two whenever you sneeze •—and the air and food passages. But the main body, the billions of useful bacteria, are in one of the lower sections of the .alimentary canal, the colon. Particles of vegetable nourishment which are enclosed in cellulose cannot be digested in the stomach. The acids will not dissolve cellulose. All this part of our food passes on to our bacteria denartment to be broken up and made available. So microbes are, like Mr Shaw’s plays, “pleasant and unpleasant”; and, like the plays, the great majority are pleasant, or at least useful. Not only these swarms in the lower regions of the body, but the vast majority of the swarms in Nature, serve a useful purpose. Bacteria belong to the plant-world. There used to be much dispute as to whether they were plant or animal in nature, but it is now the custom to hand them over to the botanist. But they have none of the green matter (chlorophyll) by,means of which plants are able to live on inorganic chemicals, and they are therefore compelled, as a rule, to live, like animals, on organic substances. Hence the curious character of the bacteria. Many of thorn are parasites on the living, bodies of animals, and these are the unpleasant microbes. It is probable that every infectious or contagious disease is due to them, though they may be so small that in a few cases the microscope has not yet discovered the “germ.” They generally make mischief by producing poisons in the blood. To-day medical science is triumphantly meeting this danger by methods which we have described in a previous article. It “tames” the virulent bacteria, and we are inoculated with billions of these to prepare for the possible advent of the “wild” specimen. The Scavengers.— But the great majority of bacteria feed on dead and decaying matter. They are the scavengers of the earth. People rarely reflect what becomes of the vast litter of dead animals, leaves, bits of pacer, flowers, straw, etc., that is strewn over the face of Nature every year. You must thank the übiquitous bacteria. Bodies would not even decay without their aid. Then there •are the still pleasanter bacteria which attend to fermentation. The “bees,” with •which so many, people are now making ■what, by a very serious stretch of language, they call wine, are clumps of bacteria, yeast, and molds—three families which are very closely related. They play a great part in brewing, wine-malnng, bread-making, tanning, cheese-making, and a hundred other things. It is a distinct type of bacillus that gives its flavour to your favourite cheese. The First Living Things.— But of late years we have discovered , other .bacteria which can feed on inorganic mattefr, and these are in a sense the most interesting of all. They are the simplest organisms known, and they suggest to us the first living things that appeared on the earth. Myriads of i them help agriculture by fixing nitrogen (from the air or from manure) and so enabling the plants to absorb it. Whole colonies of them live amicably in the roots of plants like beans and co-operate with the plants. Bacteria do not normally die. The living body splits into two living bodies, and so the chain goes on. • Some divide thus every half-hour, and the reader who cares to do a little arithmetic will see that this means that in 24 hours one bacillus (a rod-shaped bacterium) will be multiplied into several billions! The rate of increase is not phenomenally rapid in itself, but it is enough to sustain this prodigious population, in spite of man’s inroads upon it.