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PHARMACEUTICAL BACTERIOLOGY 



age the development of the particular microbes that will set free or render 

 available the food substances required by the crop plants under cultiva- 

 tion. Agricultural bacteriology is beginning to make practical use of 

 certain plant food forming microbes. Of these the free nitrogen-binding 

 microbes are most promising from the standpoint of practical commercial 

 utility, and have received much attention in recent years. The more 

 important species are: Rhizobium mutabile, Bacillus ellenbachiensis 

 Caron, Azotobacter chroococcum; Bacillus subtilis, Bacillus calif orniensis, 

 and a few others. Of these, Rhizobium mutabile, the root-nodule bacterium 

 of the Leguminosae, has received most attention. 



FIG. 51. Root nodules of sweet clover, somewhat magnified. A, rootlets with 

 nodules, a, single nodules, b, clusters of nodules. These are sometimes very large, 

 consisting of hundreds of nodules, loosely united. B, diagram of single nodule, a, un- 

 infected area, b, infected area. 



The first to suggest a plan for practically utilizing the root nodule bac- 

 teria (Rhizobia) and to secure letters patent for the process in Germany 

 and the United States, were Nobbe and Hiltner, of Tharand, Germany. 

 Patent No. 570,876 was granted Nobbe and Hiltner in the United States, 

 November 3, 1896. This patented fertilizer for leguminous plants con- 

 sisted of pure cultures of the several varieties (or perhaps species) of R. 

 mutabile, each species of plant, as bean, pea, clover, alfalfa, etc., having the 

 cultures derived from the root nodules peculiar to it. 



This commercial preparation was given the name "nitragin," and its 

 efficiency was quite carefully and extensively tested and commented upon 

 by European and American investigators. The consensus of opinion 

 seems to be that it was of doubtful practical utility for agricultural pur- 



