Part 4 (1/2)

There are still otherlost from the food cycle First, we etation result in a gradual draining of the soil and a throwing of its nitrogen into the ocean The body of any animal or any plant that chances to fall into a brook or river is eventually carried to the sea, and the products of its decomposition pass into the ocean and are, of course, lost to the soil Nohile this gradual extraction of nitrogen froe is a slow one, it is nevertheless a sure one It is far more rapid in these years of civilized life than in foriven to the city, and then are thrown into its sewage Our cities, then, with our present syste fro them away

In yet another directionlost to plant life--viz, by the use of various nitrogen colycerine, dynamite, in fact, nearly all the explosives that are used the world over for all sorts of purposes, are nitrogen coen of the coas, en The basis froen in the form in which it can be used by plants

Saltpetre, for exaunpowder The products of the explosion are gases no longer capable of use by plants, and thus every explosion of nitrogen coen products, taking the theencies contribute to reduce the a in the food cycle of Nature, and thus seem to tend inevitably in the end toward a termination of the processes of life; for as soon as the soil becoen compounds, so soon will plant life cease from lack of nutrition, and the disappearance of anien in large riculturists to purchase fertilizers The last fifteen years have shown us, however, that here again we ents for counteracting this dissipating tendency in the general processes of Nature Bacterial life in at least two different ways appears to have the function of reclai froen

In the first place, it has been found in the last few years that soil entirely free fro certain kinds of bacteria, if allowed to stand in contact with the air, will slowly but surely gain in the aen compounds are plainly manufactured by the bacteria in the soil; for unless the bacteria are present they do not accumulate, and they do accumulate inevitably if the bacteria are present in the proper quantity and the proper species It appears that, as a rule, this fixation of nitrogen is not perforanisether Certain combinations of bacteria have been found which, when inoculated in the soil, will bring about this fixation of nitrogen, but no one of the species is capable of producing this result alone We do not knohat extent these organisen fixation through bacterial life is going on It is only within a short time that it has been demonstrated to exist, but we must look upon bacteria in the soil as one of the factors in reclaien

The secondof this lost nitrogen is by a combined action of certain species of bacteria and soreen plants, as already noted, are unable to en of the ato that soumes, which contains the pea plant, the bean, the clover, etc, are able, when growing in soil that is poor in nitrogen, to obtain nitrogen frorow A pea plant in soil that contains no nitrogen products and watered ater that contains no nitrogen, will, after sprouting and growing for a length of time, be found to have accuen in its tissues The only source of this nitrogen has been evidently from the air which bathes the leaves of the plant or permeates the soil and bathes its roots This fact was at first disputed, but subsequently demonstrated to be true, and was found later to be associated with the couen from the air, it develops upon its roots little bunches known as root nodules or root tubercles The nodules are soer than this, occasionally reaching the size of a large pea, or even larger

Upon microscopic examination they are found to be little nests of bacteria In so 27)plant, and finding there congenial environment, develop in considerable quantities and produce root tubercles in the root Now, by sorowing together succeed in extracting the nitrogen fro this nitrogen in the tubercles and the roots in the foren corowth, the aen in the plant is found to have very decidedly increased (Fig 25 E)

This, of course, furnishes a starting point for the reclaiu the store of nitrogen in its roots and sterowth

Subsequently, after having finished its ordinary life, the plant will die, and then the roots and ste buried, will be seized upon by the decoen which has thus becoes already described This will result eventually in the production of nitrates Thus soain to the soil in the form of nitrates, and may now start on its route once more around the cycle of food

It will be seen, then, that the food cycle is a coredients in the soil, the food matter may start on its circulation from the soil to the plant, from the plant to the animal, froh a series of other bacteria back again to the soil in the condition in which it started If, perchance, in this progress around the circle soent, this, too, is brought back again to the circle through the agency of bacterial life And so the foodcirculation It is the sunlight that furnishes the energy for the ht that forces the food around the circle and keeps up the endless change; and so long as, the sun continues to shi+ne upon the earth there seems to be no reason why the process should ever cease It is this repeated circulation that has made the continuation of life possible for the millions and millions of years of the earth's history It is this continued circulation that makes life possible still, and it is only this fact that the food is thus capable of ever circulating from animal to plant and fro world to continue its existence But, ah we have seen, one half of this great circle of food change is dependent upon bacterial life

Without the bacterial life the aniht back again within the reach of the plant; and thus, were it not for the action of these anisms the food cycle would be incomplete and life could not continue indefinitely upon the surface of the earth At the very foundation, the continuation of the present condition of Nature and the existence of life during the past history of the world has been fundamentally based upon the ubiquitous presence of bacteria and upon their continual action in connection with both destructive and constructive processes

RELATION OF BACTERIA TO AGRICULTURE

We have already noticed that bacteria play an iricultural industries, particularly in the dairy

From the consideration of the anisms must have an even more intimate relation to the far consists in the cultivation of plants and animals, and we have already seen how essential are the bacteria in the continuance of animal and plant life But aside from these theoretical considerations, a little study shows that in a very practicaluse of bacteria, as a rule, quite unconsciously, but none the less positively

SPROUTING OF SEEDS

Even in the sprouting of seeds after they are sown in the soil bacterial life has its influence When seeds are placed erminate under the influence of heat The rich albuminous material in the seeds furnishes excellent food, and inasmuch as bacteria abound in the soil, it is inevitable that they should grow in and feed upon the seed If the moisture is excessive and the heat considerable, they very frequently grow so rapidly in the seed as to destroy its life as a seedling The seed rots in the ground as a result This does not commonly occur, however, in ordinary soil But even here bacteria do grow in the seed, though not so abundantly as to produce any injury Indeed, it has been claimed that their presence in the seed in s of the seed It has been clairowth tends to soften the foodcan more readily absorb it for its own food, and that without such a softening the seed remains too hard for the plant to use This may well be doubted, however, for seeds can apparently sprout well enough without the aid of bacteria But, nevertheless, bacteria do grow in the seed during its ger of the food ermination It may well be claimed that they ordinarily play at least an incidental part in this fundarowth of seedlings is to any considerable extent aided thereby

THE SILO

In the reat bacteriological problerown food for the winter use of his animals, he is hindered by the activity of coo decomposition and be ruined in a short time as animal food The farmer finds it necessary, therefore, to dry some kinds of foods, like hay While he can thus preserve sorowth of the farood food while it is fresh, but is of little value when dried The farmer has fro bacterial grohich enables him to avoid their ordinary evil effects This is by the use of the silo The silo is a large, heavily built box, which is open only at the top In the silo the green food is packed tightly, and when full all access of air is excluded, except at its surface Under these conditions the food reo its ordinary fermentations and putrefactions, andruined The food in such a silo may be taken out ood condition for food It is true that it has changed its character soerly eaten by cattle

We are yet very ignorant of the nature of the changes which occur m the food while in the silo The food is not preserved from fermentation When the siloxis packed slowly, a very decided ferh te is produced by certain species of bacteria which grow readily even at this high temperature The fermentation uses up the air in the silo to a certain extent and produces a settling of the material which still further excludes air The first feres occur Certain acid- producing bacteria after a little begin to groly, and in tie is rendered somewhat sour by the production of acetic acid But the exclusion of air, the close packing, and the srowth of the coood for a long ti the silo, the food is very quickly packed and densely crowded together so as to exclude asUnder these conditions the lack of ely Only certain acid-producing organisrow, and these very slowly The essential result in either case is that the co, probably by lack of sufficient oxygen and moisture, and thus the decay is prevented The closely packed food offers just the sarowth of common putrefactive bacteria that we have already seen offered by the hard-pressed cheese, and the bacteria growth is in the sae of the h to understand that the successful ement of a silo is dependent upon the manipulation of bacteria

THE FERTILITY OF THE SOIL

The farmer's sole duty is to extract food fro crops, or indirectly by raising animals which feed upon the products of the soil In either case the fertility of the soil is the fundaift to him from the bacteria

Even in the first formation of soil he is in a measure dependent upon bacteria Soil, as is well known, is produced in large part by the cruenerally call weathering, and regard it as due to the effect ofaction of the air Doubtless this is true, and the weathering action is largely a physical and chemical one Nevertheless, in this fundaration bacterial action plays a part, though perhaps a small one Some species of bacteria, as we have seen, can live upon very sien and carbonates sufficiently highly corow on the bare surface of rocks, assien from the air, and carbon from some widely diffused carbonates or from the CO2 in the air Their secreted products of an acid nature help to soften the rocks, and thus aid in perfor

The soil is not, however, all rated rocks It contains, besides, various ingredients which co these are various sulphates which form important parts of plant foods These sulphates appear to be forency The decos, to hydrogen sulphide (H2S) This gas, which is of corowth into sulphuric acid, and this is the basis of part of the soil sulphates The deposition of iron phosphates and iron silicates is probably also in a measure aided by bacterial action All of these processes are factors in the forration which occurs everywhere in Nature is chiefly the result of physical and che that the physical and cheht extent at least, assisted by bacterial life

A en content, without which it is coredients has been more or less of a puzzle Fertile soil everywhere contains nitrates and other nitrogen coe accumulations of these compounds, like the nitrate beds of Chili That they have coen seems certain, and various atteen fixation It has been suggested that electrical discharges in the air may forredients to for this to be a very important factor But in the soil bacteria we find undoubtedly an efficient agency en fixation As already seen, the bacteria are able to seize the free at it into nitrite and nitrates We have also learned that they can act in connection with legu theen and store it redient in the soil is prevented fro exhausted by the processes of dissipation constantly going on Further, by soredient to have been derived Such an organic agency is the only one yet discerned which appears to have been efficient in furnishi+ng virgin soil with its nitrates, and we inal fertility of the soil But in another direction still does the farmer depend directly upon bacteria The most important factor in the fertility of the soil is the part of it called humus This humus is very coen coar, and arden soil different from sand, or the rich soil different from the sterile soil If the soil is cultivated year after year, its food ingredients are slowly but surely exhausted

So is taken from the humus each year, and unless this be replaced the soil ceases to be able to support life To keep up a constant yield from the soil the farmer understands that he must apply fertilizers more or less constantly