376 
Bacteria their Nature and Function. 
suitable composition, found that the one is capable of converting 
ammonia into nitrites, the other these latter into nitrates. There 
can then be no doubt that the problem of the manufacture on a 
large scale of these nitrifying microbes, so important for agriculture, 
must be considered as solved. 
Bacteria of Leguminos.®. 
I have next to bring to notice a group of organisms which, like the 
former, are of interest and importance to the vegetable kingdom, at 
any rate to one portion of it, viz. the plants belonging to the natural 
order Leguminosse. 
Hellriegel and Wilfarth had shown that the excess of nitrogen 
in the Leguminosas is obtained from the atmosphere by the instru- 
mentality of bacteria in the soil around the roots of the leguminous 
plants ; that these bacteria “ fix ” the free nitrogen contained in the 
soil, derived, of course, from the atmosphere ; and that, if the soil 
be sterilised, by which the bacteria are killed, no fixation of nitro- 
gen can take place, and the growth of the leguminous plant remains 
appreciably attenuated. The roots of leguminous plants growing 
in the ordinary soil are known to possess numbers of nodular 
growths. These nodules have been thoroughly investigated by a 
large number of observers, and their importance in the process of 
fixing the nitrogen, and in the proper development of the plant, 
has been satisfactorily worked out ; foremost amongst these stand the 
investigations of Marshall Ward, of Sir John Lawes and Sir Henry 
Gilbert, of Beyerinck, Prazmowski, Nobbe, and Prank. Beyeriuck, 
then Prazmowski, and particularly N obbe, have shown that the 
nodules on the roots owe their origin to the growth in the tissues 
of the root of certain bacteria, and it is these bacteria which are 
instrumental in fixing the free nitrogen. These bacteria represent 
well-defined species, and, as Nobbe has shown, differ for the different 
Leguminosse. 
Photographs were shown to illustrate the distribution, in the 
tissue of the nodules on the roots of lupines, of particular species 
of bacteria, then the character of these bacteria under cultivations, 
and their aspect and size in microscopic specimens. This species of 
bacilli is composed of motile cylindrical rods, which, cultivated in 
gelatine, liquefy this, and produce in the liquefied gelatine a peculiar 
greenish fluorescent colouring ; on agar they also produce this 
colouring. The nature of the young colonies in plate cultivation, 
their manner of spreading and swarming, are well shown in such 
photographs. 
Chromogenic and Phosphorescent Bacteria. 
The remarkable species of what are termed chromogenic bacteria 
have the power to produce pigments, either pigments which become 
dissolved in the medium in which these bacteria grow, or which 
remain limited to the substance of the bacteria themselves. Species 
