and nitrates. The last is the form in which the nitrogen is usually taken up by the plants. On the other hand, the nitrates are themselves subject to the opposite forces of deoxidation. There are species of bacteria in the soil which reduce nitrates to nitrites, to ammonia or even to gaseous nitrogen. To recapitulate, then, there take place in the soil processes of nitrification, denitrification and also the fixation of free nitrogen. It was necessary to consider the former two, in order to understand the third. It would be out of place here to speculate upon the manner in which the soil nitrogen is oxidized; it might not be out of place here to consider the possible ways in which nitrogen is set free from its compounds, on the one hand, or is 'fixed,' on the other hand. Quite recently hypotheses have been advanced which would regard the processes of 'fixation' and of 'denitrification' as being very much related phases of the same physiological activities. The investigators who have labored in this field of research, and to whom we owe most of our knowledge on the subject, are Berthelot, Winogradsky, Beyerink and Stoklasa. Berthelot was among the first to observe that soils free from vegetation can increase their store of nitrogen. Winogradsky, after much painstaking search, isolated from the soil an organism, which, in company with two others, can grow in nitrogen-free media and fix considerable quantities of nitrogen in a short time. Beyrink, also, has isolated within the last few months several organisms that possess a similar power, and Stoklasa has done a great deal of careful work to determine just how the fixation of nitrogen is accomplished. Moreover the subject has assumed more than a mere scientific interest within the last three or four years. The firm of Friedrich Bayer and Co., of Elberfeld, Germany, has placed on the market a bacterial culture bearing the fancy name of 'Alinit.' This alinit they claim can under favorable conditions increase the yield of non-leguminous crops 40 per cent. On examination, the alinit proved to be a pure culture of B. ellenbachii, mixed with a starchy material resembling dried and pulverized potatoes. The organism was isolated by a German gentleman-farmer, Caron by name, and named B. ellenbachii after his estate, Ellenbach. This bacillus differs but little from the organism isolated by Du Bary some years earlier, and called by him B. megaterium. This organism, Stoklasa claims, is not only similar to, but identical with B. ellenbachii. The accumulated evidence of several investigators on this point inclines me to the belief that the two are not identical, though very much allied. At any rate, Stoklasa has shown that B. megaterium is capable of fixing atmospheric nitrogen in media containing but traces of fixed nitrogen; it develops and adds to the nitrogen content of the medium by drawing upon the nitrogen of the air. This organism has, as it were, a double nature. In the first place, as just noted, it is capable of fixing atmospheric nitrogen; in the second place, it exerts
