Two Unseen Friends: A Study in Agricultural Science

TWO UNSEEN FRIENDS.

BY DR. JOHN A. WIDTSOE, DIRECTOR EXPERIMENT STATION, STATE

AGRICULTURAL COLLEGE, LOGAN, UTАН.

More than two hundred years ago there lived in the ancient city of Delft, in Holland, a janitor to the central city court, who was known as Anton Leeuwenhoek. In his youth he had been apprenticed to a commercial house in Amsterdam, but he had soon tired of the life, for he possessed an inquisitive mind which was constantly seeking the explanations of the strange phenomena of nature; and the life of a merchant gave him no leisure for find- ing answers to the questions. So he sought the humble position of a janitor in his native city, in order that he might have some time for the study of nature, and that he might please himself under the influence of the spirit of knowledge-seeking which is character- istio of the school room. In this position, he worked faithfully for nearly forty years. During his spare moments, he pursued with won- derful industry the study of nature, and pursued it so intelligently that, in spite of his lack of scholastic training, he gave to man- kind the knowledge of a new world, which up to his day had been dreamed of only by the most fanciful of thinkers. And this new world, opened to us by the humble Dutchman of Delft, has given to humanity a greater power over the conditions of nature than, perhaps, has any other branch of knowledge. In his youth Leeuwenhoek had learned the art of making and polishing magnifying glasses; and when he settled down at Delft, he devoted himself to making the very best magnifying glasses possible, and to using these magnifiers in the study of the minute

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structures of nature, such as the wings of mosquitoes and the "stings" of bees. In time, he acquired great skill in the making of powerful lenses, and in fact, constructed the first really good microscope. It occurred to him once, to examine with his micro- scope some rain water which had been standing in an open vessel for several days, and he saw in it, to his great astonishment, thou- sands of moving, living things, which were thousands of times smaller than the smallest forms of life known up to that time. This led him to suspect the existence of a world of the extremely small, even as the extremely great was known in the heavenly bodies. He therefore carried on his researches, and examined un- der the microscope, water in which pepper had been steeped, ma- terial taken from the intestines of various animals, the crust on teeth, and many other similar substances. Invariably, he found that they contained minute organisms which moved about with great energy. One of his own descriptions reads as follows :* "I saw with very great astonishment, especially in the material men- tioned, (taken from the teeth) that there were many extremely small animals which moved about in the most amusing fashion; the largest of these showed the liveliest and most active motion, moving through rain-water or saliva like a fish of prey darts through the water: this form, though few in actual numbers, was met with everywhere. A second form moved around, often in a circle, or in a kind of curve; these were present in greater numbers. The form of a third kind, I could not distinguish clearly; sometimes it appeared oblong, sometimes quite round. They were very tiny, in addition to which they moved forward so rapidly that they tore through one another. They presented an appearance like a swarm of midges and flies buzzing in and out between one another. I had the impression that I saw several thousands in a single drop of water or saliva which was mixed with a small part of the above named material, not larger than a grain of sand, even when nine parts of water or saliva were added to one part of the material taken from the teeth." These simple, though wonderful, observations became the foundation upon which scores of able men have built the great

• Quoted by Woodhead, Bacteria and their Products, p. 50.

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science of bacteriology. The minute living forms which Leeu- wenhoeck saw were the bacteria of the present day. The purpose of this article is to discuss briefly two forms of bacterial life which have a direct bearing on the welfare of the humanfamily. We are familiar with the fact that hundreds, perhaps thou- sands, of kinds of bacteria exist. We know that many kinds of fermentation, as well as the putrefaction of dead things, are due to the action of the bacteria; and that milk sours, that cheese ripens, that butter receives its flavor, from the growth and devel- opment of special kinds of bacteria. A majority of the diseases to which man and the lower animals are subject, are caused by bacteria which enter into the blood or tissues of our bodies and grow and increase there until the organs are poisoned beyond their power of resistance. Instances of such diseases are smallpox, consumption, typhoid and scarlet fevers, and blackleg in cattle. It has been shown that in nature, bacteria are found almost every- where; that they are concerned to a certain degree with every change to which organic nature is subject; and, that in spite of their individual minuteness, they are as important in nature as the forces which are more directly evident to our senses. To understand why such minute organisms can affect our lives seriously, it is necessary to know the nature of their growth and reproduction. Under favorable conditions of temperature and food, bacteria grow very rapidly. When an organism has become about twice its original size, it contracts near the middle, pretty much as a figure 8, and finally breaks into two parts. In a short time each of these parts grows to twice its original size, and finally breaks into two parts. This process is continued forever, if all the conditions of growth remain favorable. A simple calcula- tion will show to what inconceivable results this process of division leads.* Let us assume that a bacterium is divided into two parts in one hour; that these two are divided into four by the end of the second hour, and that the four yield eight by the end of the third hour. If this process of division is continued, we shall have at the end of twenty-four hours, a number of bacteria amounting to *Dr. F. Cohn, "Uber Bakterien," p. 8.

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sixteen and one half millions ; at the end of two days, two hundred and eighty-one and one half billions, and at the end of three days, four thousand seven hundred and seventy-two trillions! Such numbers transcend the human understanding; but it is possible to make them somewhat more comprehensible by using a different method of comparison. If we assume that the great oceans cover two-thirds of the earth's surface, and that their aver- age depth is one-half geographical mile; the space occupied by the oceans would amount to 3,086,833 cubic miles. One bacterium in- creasing in the manner above described, would fill in four and one- half days all the oceans of the world. Or, the weight of the bac- teria resulting from one germ, would, at the end of three days, amount to 80,224 tons. Areasonable question now is, why are not the oceans and the waste places of the earth filled with a mass of bacteria? The answer is, simply, that the bacteria, as all other living organisms, need food in order to live. But the food supply of the earth is limited, and all life is struggling to gain as much of it as possible. In the struggle for existence, the bacteria obtain a small portion, by which their numbers are limited; they cannot increase beyond their food supply. Besides, the food in passing through bacteria is changed into substances which are harmful to bacterial life. If, therefore, the waste matters are not removed, they of themselves will destroy further life activity. Of great importance is the fact that each kind of bacterium has a special kind of work to do, and cannot, with any success, do any other kind. For instance, the germ which causes consumption in one person, under known conditions, produces only consumption in others; the diphtheria germ produces only diphtheria; the fer- ment which produces flavor in butter, produces only one kind of flavor, and so on.. This law is valuable, in that we know with great certainty what certain bacteria will do under given conditions, if we have studied their ancestors. We have often heard that nature was made for man, or that man is made to take advantage of every peculiarity found in nature; and nowhere is this more strikingly shown than in the relation of two kinds of bacteria to the life of plants. We shall meet in this study one of the most marvelous instances of perfect adaptation

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betweenman, or the wants of man, and that part ofnature which is not man. All growing plants require as food certain substances most of which are obtained from the soil. Among the necessary plant foods the element called nitrogen is of first importance. In nature, nitrogen is very abundant, for four-fifths of the air we breathe is composed of it. Plants cannot use it, however, in spite of its great abundance, except when it is combined with other sub- stances. The immense quantities in the air, therefore are directly valueless to vegetation. In order that plants can make use of nitrogen as a food, it must be in the form of nitrates, which are represented by the well-known substance, saltpeter. These nitrates occur in the soil in very small quantities ; the whole nitrogen con- tent of a fertile soil amounts to only one or two parts in a thou- sand parts ofsoil. Since this small quantity of nitrates is rapidly usedby plants, and, further, since much is lost by being dissolved and drained away by irrigation water, it is important to know how the nitrates may be restored to the soil, and the field or farm thus be kept productive. In all cultivated soils there remains, from the roots and stub- ble of previous crops, considerable quantities of organic substances which contain much nitrogen. The nitrogen in these vegetable remains, however, is not in the form of nitrates, but is locked up in compounds which the plant cannot use. As these organi re- mains are left in the soil, they begin to decay ; if left long enocugh , the nitrogen passes off from them as ammonia (which is another compound of nitrogen) and is lost. But in fertile soils, which havebeen properly treated, the decay is not allowed to go on that far, because a living organism, a bacterium, known as the nitri- fying organism, takes hold of the nitrogen when in its first stage of decayand eats it. As the nitrogen passes through the body of this organism, it is changed into nitrates, and is then in a form suitable for the feeding of plants. It has been observed frequent- ly thatmany soils in the springtime, when the melting snow soaks throughthe ground, contain practically no nitrates; but at mid- summer, the same soils carry a large quantity. This increase rep- rese nts, of course, the activity of the nitrifying organism during the mouths of warm weather.

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As this subject is of great practical importance as well as scientific interest, it will be profitable to consider the conditions under which this organism will best perform its work-the pro- duction of nitrates for the plant. First, it requires food. Roots, or stubble, or manure, and all decaying vegetable matter, suit its taste. The temperature must be of a proper degree-about the heat of a warm summer day. That means that in wet, cold soils the organism will not flourish. Then the soil must not be sour; lime added to a sour soil will sweeten it. Finally, there must be a circulation of air around the soil particles. This is provided for by frequent tillage or hoeing. If all these conditions are observed, the nitrifying organism will flourish, and change the inert stubble of one year's crop into food for the living crop of the next year. It is interesting to recall, in this connection, the use to which several of the governments of Europe put this organism, some fifty or one hundred years ago. In those days, nitre, which is a necessary constituent of gunpowder, was not so common as it is today; and, as gunpowder is essential to modern warfare, Switz- erland, Sweden, and other European countries, imposed anitre tax on every land holder in the country. The law prescribed that every man who owned land should pay a certain number of pounds of nitre for every acre of ground owned. Nitre is a nitrate a compound of potash and nitric acid. Potash is found in abundance in wood ashes. To make the nitric acid the farmer gathered the manure of his stables into large heaps, added to them straw and lime, and drenched them occa- sionally with liquid manure or with water. In the course of a year, the manure heaps were leached, and the leachings were found to be heavily charged with nitric acid held in combination by lime. Potash was then added, and pure nitre crystallized out. In this process, the nitrifying organism acted on the nitrogen of the manure to change it into nitric acid. The straw was added to make the mass porous, in order to allow air to enter; and the lime was used to prevent the mass from becoming too sour for the bacteria to thrive, and to fix or neutralize the acid as fast as it was produced. In this way the farmers paid to the government every year thousands of pounds of nitre. The same process is

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going on today in every soil which contains decaying vegetable matter. This discovery when made, gave the farmer an unsuspected power over his land; since, by proper treatment, he could encour- age the growth of the nitrifying organism, and consequently, in most cases, ensure heavy crops. As crops are grown on a piece of land and removed, more or less nitrogen, which the plants have taken from the soil, will also be removed; and, in course of time, unless the soil is manured, there will be no nitrogen left for the bacteria to change into ni- trates. In other words, the soil will be exhausted. Many of the desert soils of Utah are of this nature also, and refuse to grow crops, until nitrogen is added to them in some form. Centuries ago, however, it was observed that on such exhausted lands, which refused to grow wheat or oats, or potatoes, large crops of clover or lucern, or peas or beans, could be raised without any manuring. Many Utah farmers have had a similar experience. Lands on which wheat could not be grown, gave heavy yields of lucern; and after a few years, when the lucern was plowed up, heavy crops of wheat could be raised on the same ground. The reason for this observation seemed an unfathomable mystery for many years ; and eminent investigators studied the problem only to give it up in despair. It is only some fifteen years since a German scientist, Hellriegel, succeeded in explaining satisfactorily why lucern or clover will grow where wheat or oats will not. His discovery has become fundamental in the modern science of agriculture, and is justly ranked as the greatest discovery in its domain of the last quarter of a century. Hellriegel observed on the roots of growing clover, lucern, peas or beans, numerous small swellings, sometimes attached to the roots directly, and sometimes attached by a comparatively thin and long fibre. These swellings, it has been learned, are caused by countless colonies of bacteria, that are really parasites on the plants. But they possess a marvelous property which is of value to the plant. They have the power, namely, of taking the free nitrogen as it is found in the air, and of changing it into forms suitable for plant life. From the juices of the plant, they take some nourishment, but in return they eat the nitrogen of the air,

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and give it to the plant on which they live. There is thus a mu- tual exchange,both the plant and the organism profiting by it. Investigation has shown that this organism can live only on the roots of plants which carry their seeds in pods-called leguminous plants-such as lucern, peas or beans. Hence, by growing peas on a soil which is so poor in nitrogen that wheat will not grow there, it is possible to take nitrogen from the air, and to store it in the leaves, stalks and roots of the crop. The roots and stub- ble left when the peas are removed, will then furnish nitrogen, for the next year's crop of wheat or oats. This, too, explains the value of green manuring. If a soil has been worn out by many crops of wheat, and lacks nitrogen, then peas or clover, or some other pod-bearing plant, should be planted. After the crop has gathered considerable nitrogen from the air, it is plowed under, thus enriching the land immensely. This, then, is the brief story of two bacteria upon the activ- ity of which mankind depends in a very great measure for his bread and butter. It is true that several loathsome diseases to which man is subject, are caused by bacteria; but much of the good which nature offers us is also wholly due to similar minute forms of life. Bacteria have a bad reputation; it is unfounded prejududice; they should be held in high esteem. Discoveries, such as here discussed, have changed, during the past fifty years, the ancient imperfect art of farming into the modern, noble science of agriculture-a science worthy to be placed by the side of any of the learned professions. It is by such knowledge that man shall grow in power until he can bend the earth to his will. It is by such careful study as led to the dis- covery of these two organisms, that wisdom comes. Above all, is it not a good God, who has made the world so that in any walk in life we may find in nature material for noble thoughts to satisfy the cravings of our minds; who has given the husbandman such wondrous truths to contemplate, as he scatters the seed upon the spring-awakened ground ?