Page:Popular Science Monthly Volume 90.djvu/382

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Man's Invisible Friends and Foes

��They were no more cheated to do us harm than were other forms of plant or animal life. If they had their choice they would never enter our bodies at all

By R. L. Kahn

WE and the bacteria are close neighbors. Our homes are their homes and wherever we go, they go. But alas! How we misunder- stand their purpose.

Not long ago, I heard a lecture on these neighbors of ours. The speaker discussed a number of diseases in which bacteria play a part. I do not recall the details, but the impression left I remember well. It was that bacteria are our worst enemies.

It is well to emphasize the relation of bacteria to disease, but it is important that their relation to health be emphasized also. Their purpose seems to be not to cause disease and death but life and health. Remove bacteria from the world, and life might soon cease. Let them stop work, and plants and animals might starve to death.

Perhaps no other organisms play a more important role in the evolution of plant and animal life than bacteria. It seems truly inconceivable that organisms so minute should be capable of bringing about such profound changes in every phase of life. Tasks which the greatest chemists cannot perform they carry out with ease.

What Bacteria Do for the Farmer

The study of modern agriculture is largely the study of the bacteria of the soil. Decaying organic matter in the soil is transformed into food for plants by bac- teria. Three types of these organisms supply plants with nitrates. One type transforms organic matter into ammonia, another changes the ammonia into nitrites and still another changes the nitrites into nitrates. Such is the division of labor that each kind of bacteria attends to its own specialty.

One of the products of decay is a gas- sulphuretted hydrogen. The sulphur bacteria decompose this gas and store up free sulphur in their own bodies. But the

���supply of sulphuretted hydrogen is soon ex- hausted. The bacteria perish and free sulphur is liberated. Ultimately we get sulphate of lime, an important constituent of plant food. There are also bacteria which supply plants with iron, and count- less others which help in one way or another to make plant life possible.

If it were not for bacteria, the world might be piled up with dead plants and animals. Bacteria are the scavengers of the living world. As soon as the life of an animal or plant ends, bacteria gather around it, take the body apart, and reduce it to the elements of which it was originally built.

This inherent power makes bacteria per- petuators of life. Matter, we know, is indestructible. The elements which go to build up an animal or plant are not in any way affected when the animal or plant dies. Let these elements be set free, and Nature will utilize them for the construction of other living bodies. To bacteria it is given to supply Nature continually with elements so that she may always build new living structures.

Are Bacteria Necessary to Health?

Whether or not health is possible with- out bacteria is to-day one of the most interesting problems in the field of biological science. The question is far from settled. Nuttal and Thierfelder, two well-known scientists, believe that it is possible for animals to live and retain their health with sterilized air, food and water. Some famous experiments carried out by Cohendy and Wollman at the Pasteur Institute, Paris, also seem to indicate that animals

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