DEPARTMENT REPORTS. 49 



"The bacteriologist has not confined his labors to the study of those 

 micro-organisms which cause disease, but he has gone farther and has 

 shown that some of these minute forms of life which we call germs are 

 capable of rendering great service to mankind. Only a few years ago 

 it was believed by many scientists that the amount of combined nitro- 

 gen in the world is constantly decreasing, and that neither plants nor 

 animals are capable of utilizing the free nitrogen in the air. It was 

 therefore supposed to be a necessary conclusion that life on this planet 

 must cease as soon as all the combined nitrogen is used up. It was 

 stated that the explosion of every ounce of gunpowder, whether the pro- 

 jectile which it carried struck a living object or not, carried death with 

 it, inasmuch as it lessened the sum total of combined nitrogen in exist- 

 ence. The bacteriologist by his investigations has shown that this state 

 of affairs is not so bad as was once believed. He has demonstrated that 

 there are certain micro-organisms gi'owing on the roots of certain plants, 

 and that by the combined action of the germ and the plant free nitrogen 

 may be taken from the air and utilized in building up plant tissue or 

 in other words, that it may be changed from the free to the combined 

 form, and when thus changed, it may subsequently be used for food by 

 either plants or animals. This is what is known as the process or 

 function of fixing nitrogen, and it depends upon the combined action 

 between certain germs and leguminous plants. About 20 years ago it 

 was quite conclusively shown that peas, beans, and other legumes 

 when grown in a soil wholly free from nitrogen were capable of con- 

 structing nitrogenous compounds and building up nitrogenous plant 

 tissue, while the only source of the nitrogen thus utilized was that 

 existing free in the atmosphere. At first this view was believed to be 

 founded upon faulty observatioUvS, but thorough experimentation has 

 shown that the statement made above is a fact. Then men set about 

 to ascertain the conditions under which plants, and especially legumi- 

 nous plants are able to utilize the free nitrogen of the atmosphere. 

 These experiments were conducted by skilled botanists in various parts 

 of the world, and now after 20 years of these labors it can be positively 

 stated that the manner in which leguminous plants convert nitrogen 

 into compounds has been discovered. If the roots of a leguminous 

 plant be studied, they will be found to be dotted with tiny nodules, 

 which are known to the botanist as tul)ercles, but which, however, have 

 no relation to the ])athological conditions known to the medical man 

 under the same name. These tubercles or swellings on the roots of 

 the pea vine vary markedly in size. They may be so small that they 

 are barely discernible to the naked eye, and in some instances they 

 have a diameter of one-sixth of an inch or more. Of course the exist- 

 ence of these nodules on the roots of leguminous plants had long been 

 known, but their function was not understood. It was generally be- 

 lieved that their presence indicated a diseased condition, but it was 

 found that the plants on the roots of which they developed most abund- 

 antly thrived most vigorously. I shall not attempt before this audi- 

 ence, in which there are many who know more about this subject than 

 I do, to go into detail concerning the relation of these tubercles to the 

 fixation of nitrogen by leguminous plants. Suffice it to say that experi- 

 mentation has shown that these nodules do not form on the roots of 

 plants gTown in sterilized soils, and that under the same conditions 

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