May 6, 1892.] 



SCIENCE. 



263 



dustry of the world has been drawing for years, and will continue 

 to dratv until they are exhausted. But these sources are far away. 

 The nitrogen that we get from them is very expensive, and the 

 stoi'e is very limited in quantity. We can see in the not very dis- 

 tant future the complete exhaustion of all these nitrogen beds. 

 Tbis has led scientists to look with a considerable degree of dis- 

 may upon the future of the vegetable world. What is going to 

 happen when all the available nitrogen is used up? If we are 

 going to continue lo take the nitrogen from the soil, and throw it 

 into the ocean, we will soon exhaust the soil, and if there is no 

 store of nitrogen anywhere for our plants to draw upon, what are 

 ■our plants going to do in the future ? 



Now, there is a store of nitrogen in the world which is abso- 

 lutely unlimited, and that is in the air that surrounds us. The 

 air that we breathe is made up of four parts of nitrogen and one 

 part of oxygen. There are quantities of nitrogen everywhere if 

 the plants could only get hold of it, but it has been thought that 

 plants cannot feed on the nitrogen in the air at all. Experiments 

 have been carried on for a great many years to find out whether 

 plants could not in some way or other get hold of the nitrogen of 

 the air. If we could only prove that our plants can get hold of the 

 nitrogen in the air then the problem is solved. But the experi- 

 ments which have been carried on year after year have seemed to 

 demonstrate that plants cannot use the nitrogen of the air for 

 food, that it is not in a condition in which they can get hold of it. 

 About ten years ago, however, certain experimenters in this country 

 and in Europe found that in some of their experiments plants did 

 in some way get bold of nitrogen from some source when it was 

 not fed to them; that a plant could be grown in sand absolutely 

 free from nitrogen, and yet in some way that plant got hold of 

 nitrogen ; the only source for it was out of the air. That led to 

 further experimentation until within the last four or five years 

 the results have all been pointing in one direction. They seem to 

 show us that there is one family of plants, at least, which is capa- 

 ble of getting hold of nitrogen out of the air. This is the plant 

 family to which the pea, the bean, and the clover belong. It is, 

 in general, the pea family — the Leguminosce family of plants. 

 This family of plants in some way does succeed in getting nitro- 

 gen from some source when we do not give it to them as food, 

 and it must be that they get it from the air. And yet those ex- 

 periments are entirely contradictory to the earlier experiments, 

 which seemed to show that plants could not get hold of nitrogen 

 in the air. The explanation was not found until a few years ago. 

 Two or three years ago some experiments were performed in Ger- 

 many which have finally led to the solution of the problem, at 

 least in part, and, curiously enough, we find that the whole secret 

 of the matter is connected with these organisms which I am dis- 

 cussing this morning. It is to bacteria that we owe this power 

 which is possessed by plants of the pea family to get hold of 

 nitrogen. If you plant peas in soil containing a certain species of 

 bacteria, or at least certain species of micro-organisms, these 

 micro-organisms crawl into the roots of the pea, and then begin 

 to multiply inside the roots. The little roots begin to swell and 

 there appear upon them a lot of minute nodules, which have re- 

 ceived the name of " root tubercles." If I am not mistaken, some 

 of those little root tubercles were shown to the meeting here last 

 evening. These root tubercles, as I say, make their appearance, 

 and it is found that wherever these root tubercles do make their 

 appearance the plant gets hold of nitrogen and grows well. 

 Where these root tubercles do not njake their appearance the plants 

 are unable to get hold of nitrogen unless it is fed to them. Now, 

 these root tubercles are produced by bacteria, and these root tuber- 

 cles are the agencies by which, in some as yet unexplained way, 

 "the pea gets nitrogen out of the air. 



Thus you see that in the final analysis of the life of a plant, in 

 the assimilation of nitrogen from the air, we are brought to the 

 conclusion that it is the agency of these minute microscopic organ- 

 isms that is the source of the assimilation of nitrogen from the 

 air by plants. Thus we owe the growth of these plants to bac- 

 teria. How the bacteria get the nitrogen out of the air has not 

 yet been explained. 



Even before the scientists made this discovery, the farmer had 

 ■made the discovery practicallj' on his farm. You have known 



that you could, in some, to you inexplicable, way, rejuvenate an 

 old worn-out soil by cultivating clover upon it, or by cultivating 

 beans. That has been the practice of farmers for years. It has 

 been found that in some way the cultivation of clover, instead of 

 exhausting your soil as the cultivation of some plants does, really 

 increases the fertility of the soil. You cultivate your clover for 

 one season, then the next season you plow the roots into your soil, 

 and you find the field will produce a better crop than before. 

 This result is brought about through the agency of these organ- 

 isms. The clover belongs to the family of peas, and clover is one 

 of the plants that this particular species of bacteria that I am 

 speaking of can attack. The bacteria in the soil get into these 

 roots, grow in them, produce these root tubercles, and by means 

 of these the clover gets nitrogen out of the air and stores it up in 

 its roots. The next season you plow the roots into the soil, and 

 then come the nitrifying bacteria which pull the roots to pieces 

 and decompose them into the condition of nitrates, and then the 

 next seasop the plant which you sow gets hold of the nitrates 

 which came from the roots of the clover and which has been brought 

 there through the agency of these bacteria. You see, then, that 

 the farmer owes everything to the bacteria. 



I think you will find that I am justified in the statement I made 

 at the beginning, that the study of bacteriology to-day is even more 

 truly a department of agriculture than of medicine. The bacteria 

 belong to the farmer more truly, or at least as truly, as they be- 

 long to the physician. 



Now, I must draw my remarks to a close. Let me, in conclu- 

 sion, say that we must not think too hardly of bacteria. It is true 

 they are the causes of evil, it is true that they produce disease, 

 but it is also true that they do good. It is true that they are our 

 enemies, but it is also true that they are our closest allies. It is 

 true that without them we could not have our small-pox nor our 

 yellow-fever, we could not have our diphtheria or our scarlet-fever, 

 neither could we have the epidemic which is at present going over 

 this country, nor, in fact, should we have any of our epidemics, 

 were it not for the bacteria. But when we remember that it is 

 through the agency of these organisms that we bake the loaf of 

 bread that comes on to our table, that it is through their agency 

 that the immense brewing industries are able to exist, that it is 

 through their agency that the industries connected with the manu- 

 facture of alcoholic liquors are possible; that without them we 

 could not get our vinegar or our lactic acid ; that without them we 

 could not make our ensilage; when we remember that these bac- 

 teria give the butter-maker the aroma of his butter; when we re- 

 member that it is the decomposition products of the bacteria that 

 the cheese manufacturer sells in the market;- when we remember 

 their agency as scavengers, how it is that they keep the surface of 

 the earth clean and fresh and pure and in a constant condition for 

 the continued growth of plants; when we remember their value to 

 the soil in decomposing the dead bodies of animals and plants, and 

 thus enabling the same material to be used over and over again 

 for the support of life, and hence making possible a constant, per- 

 petual condition of nature; and when we remember, lastly, that it 

 is only through their agency that plants were originally enabled to 

 get hold of nitrogen at all, and that it is only through the agency 

 of these bacteria that we may hope for a continuance of a supply of 

 nitrogen to the soil, — when we remember all these things, I think 

 we will recognize that the power of the bacteria for good far out- 

 weighs their power for evil. Without them we should not have 

 our epidemics, but without them we should not exist. Without 

 them it might be that some individuals would live a little longer, 

 if we could live at all. It is true that bacteria, by the produc- 

 tion of diseases once in a while, cause the premature death of an 

 individual; once in a while they will sweep off a hundred or a 

 thousand individuals, but it is equally true that if it were not for 

 them, plant life and animal life would be absolutely impossible on 

 the face of the world. 



The Grand Honorary Walker Prize of the Boston Society of 

 Natural History, a sum of one thousand dollars, has just been pre- 

 sented to Professor J. D. Dana of New Haven. Previous recipients 

 of the prize have been Dr. Joseph Leidy, Mr. Alexander Agassiz, 

 and Professor James Hall. 



