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SCIENCE. 



[Vol. XIX. No. 483 



inorganic compounds like these phosphates and sulphates and 

 potassium salts, etc., and the plants serve as a means of communi- 

 cation between animals and the inorganic world, for the plants 

 take these inorganic materials and make them into something 

 which we can use as food. Plants, then, are the means which we 

 have of making use of inorganic nature ; or, in other words, the 

 whole animal kingdom is parasitic upon plants. But plants are 

 in their turn utterly unable to live upon animal foods. A plant 

 cannot feed upon albiimen, a plant cannot eat starch, a plant can- 

 not eat sugar, a plant cannot eat fat; plants are unable to use the 

 foods that animals use, and when the body of a plant dies, although 

 it is in a condition to be used as food by animals, it is not in a 

 condition to be used again as food for plants. The dead body of 

 the bird is in a condition in which plants cannot make use of it 

 at all. A plant cannot use the albumen of the bird's tissue; a 

 plant cannot use the fats in an animal; a plant cannot feed upon 

 the sugars that are in the dead sugar-canes; a plant cannot 

 feed upon the slarches or the cellulose that is in the body of the 

 dead tree. Nevertheless, the plants do succeed in getting hold of 

 this food, and it is through the agency of these bacteria that we 

 are speaking of this morning that they do it. Just as soon as the 

 body of an animal or plant dies, the bacteria get into it, begin to 

 grow in it, decomposing it, and pulling it to pieces. They pull 

 the starch to pieces, they pull the sugar to pieces, and albumens 

 and fats share the same destruction. Little by little they take 

 those compounds which plants cannot feed upon, and, by shaking 

 them to pieces, bring them down to simple combinations which 

 plants can feed upon. 



Of special importance is one particular kind of organism known 

 as " the nitrifying organism," which produces nitric acid. Plants, 

 as I have said, cannot feed upon such things as albumen. The 

 putrefying bacteria can decompose albumen and break it up into 

 certain simple compounds, but ordinary putrefying bacteria are 

 not able to break that albumen down far enough for plants to get 

 hold of it. Plants have got to live upon such things as nitrates 

 and salts of nitric acid. Now, there is one sort of bacteria living 

 in the soil which gets hold of the albuminous compounds and 

 forms nitric acid. This is the nitrifying organism, and the nitri- 

 fication is the last stage in the decomposition process by which an 

 albuminoid is converted into a condition in which plants can get 

 hold of it. One practical application of this you are all familiar 

 with in the ripening of fertilizers. You know that green manure 

 is of absolutely or of practically no use as a fertilizer on your fields. 

 You know that it must 6rst stand for a while and ripen, or '■ rot." 

 as you call it. Now, what is taking place in that fertilizer while 

 it is ripening ? Simply the series of ctanges that have been men- 

 tioned. That fertilizer contains chemical compounds of a high 

 degree of complexity, compounds that the plants cannot feed upon ; 

 they are too highly complex for plants to use as food. Bacteria, 

 however, get into that heap and begin to grow in it; and, as the 

 fertilizer becomes ripened, these high chemical compounds are 

 pulled to pieces, they become converted into simpler decomposition 

 products, and eventually, if the ripening is continued long enough, 

 the fertilizer is in a condition fit for the fields. Now, when put 

 upon the fields, the plants can get hold of the material. You will 

 see now what I meant when I stated at the beginning of my lec- 

 ture that in spite of all the cultivating that you and your horses 

 might do in the fields, it would be useless without the agency of 

 these organisms. You might put on your fertilizer; but, if that 

 fertilizer is not acted upon by bacteria, it will be of no use, and 

 thus the bacteria come in to complete the operation which you 

 began. You do your duty and the bacteria do theirs, and the 

 consequence is, the fertilizers which you are using are brought 

 into a condition in which the plants can get hold of them, and 

 thus the food of plants is produced. You see, then, that in this 

 way plants and animals are able to use over and over again the 

 same material. The plant gets this material out of the soil and 

 out of the air; the animal comes along then and feeds upon the 

 plant; then the animal dies, and the plant dies, and the bacteria 

 get into the body of the animal or plant, pull it to pieces and pro- 

 duce from it decomposition products, and they get into the soil in 

 the form of nitrates and nitric acid compounds ; or they go off into 

 the air in the form of ammonia and carbonic acid. The bodies of 



these animals and plants are thus reduced to simple conditions, 

 and now the plants once more get hold of them, and use as food 

 the same material that previous generations used. Thus over and 

 over again the same material is used, and thus nature is kept per- 

 petual. This is the explanation of the constant, perpetual growth 

 in nature. This is the reason that nature does not exhaust itself. 

 This is the reason that animals and plants have been enabled to 

 grow upon the surface of the earth for the past hundreds and hun- 

 dreds of centuries. 



But this is not the end of the agency of bacteria in plant life. 

 They are not only of value in ripening your fertilizers and in 

 keeping up this constant growth of nature, but we have learned 

 within the last two or three years that at the very foundation the 

 growth of plants is absolutely dependent upon these organisms, 

 and similarly in the future the continuance of the vegetable world 

 must be also dependent upon them. I have stated that nature is 

 perpetual because the same material can be used over and over 

 again. That is true in a sense, but not true completely, for you 

 will see with a little thought that little by little the soil is being 

 drained of its food, little by little the materials in the soil are 

 being turned into the ocean. A tree grows, takes out of the soil 

 its food, and finally dies. If it falls on to the ground, as I have 

 described, the bacteria get at it and grow there until the tree 

 eventually becomes wholly incorporated into the soil so that it can 

 be used once more as plant food. But it may be that the tree instead 

 of falling in the forest falls into a river, drifts down the river, 

 begins to decay, and eventually goes into the ocean. After the 

 products of decomposition are passed into the ocean, there is no 

 getting them back to the soil. "The sea will not give up its 

 dead," and the ocean does not give up the nitrogen and the other 

 salts that are gradually being carried to it by this process. Or, 

 again, a plant gi-ows and produces wheat, produces fruit, produces 

 nuts, and the grain, the fruit, and the nuts are taken to the city to 

 be used as food for men. The food is used by men, and most of 

 it eventually gets into the sewage of the city, is carried down to 

 the river, and from the river it is carried into the ocean. So here 

 again through the sewage of our cities the foods which are sup- 

 plied to our cities are being thrown into the ocean, and thus the 

 soil is being drained of its foods. This process is not a rapid one. 

 It is only slowly that the foods are being taken out of the soil and 

 carried to the ocean. Nevertheless, it is the constant dropping 

 that wears away the rock, and it is easy for us to see that if this 

 process goes on age after age, our soils are inevitably doomed to 

 exhaustion. You know that many fields have become sterile, that 

 many farms have been worn out, that many gardens are becoming 

 infertile. You cannot cultivate your fields as you used to without 

 furnishing them food. In the Old World this is quite noticeable. 

 Although the constant draining of the soil by these agencies is a 

 slow one, it is a sure one, and if there is no way of getting nitro- 

 gen and other salts back from the ocean to the soil, it would seem 

 that the life of all vegetation is inevitably doomed to exhaustion, 

 and with the life of vegetation the life of animals must cease, the 

 whole living world must end. 



When the scientist observed this fact, he immediately looked 

 around to see if there was not a remedy for it. Now, as far as 

 some of the plant foods are concerned, there does not seem to be 

 any occasion for fear. The phosphates, the sulphates, and the 

 potassium salts, which are plant foods, seem to exist on the sur- 

 face of the earth in almost unlimited quantities. There have been 

 immense amounts of these salts found in certain parts of the world, 

 and they can be mined at very small expense; they can be taken 

 all over the world and put directly upon the soil, so that the sul- 

 phates, phosphates, and potassium salts are in practically unlimited 

 quantities. We have no fear so far as they are concerned. For 

 an indefinite number of ages to come there is plenty of this sort 

 of food on the surface of the earth for us to supply to the soil. 

 But that is not true of the nitrogenous foods. Of course, every 

 farmer knows to-day that nitrogenous food is one of the very 

 essential foods of plants, and it is not true that there is an un- 

 limited quantity of nitrogenous salts anywhere in the world. There 

 are few sources of nitrogen other than the soil. The chief one is 

 the guano beds in the South Pacific. These are sources of nitro- 

 geneous compounds, and upon these sources the agricultural in- 



