May 25, 1893] 



NATURE 



show you here give an exact representation of these cylindrica' 

 and thread lil<e forms observed in early gelatine plate cultures ; 

 later on, when the growth has proceeded for some days, and the 

 gelatine has almost entirely become liquefied, the majority of 

 the individuals are very short — either coccus-like or short ovals. 



It is on account of this unstable or protean character of its 

 form that Hauser gave it the name of Proteus, and bein? the 

 common microbe of putrid decomposition, he called it Proteus 

 vulgaris. 



This organism, as a first and important action, peptonises 

 albumen and liquefies and peptonises gelatine ; then this peptone 

 is decomposed, yielding, amongst other substances, leucin, 

 tyrosin. indol, skatol, phenol, and further, ammonia. 



(/;) TIic Bacillus coli. — The normal inhabitant of the intestine 

 of man and animals is another powerful albumen decomposing 

 microbe, but, unlike the proteus, it decomposes albumen with- 

 out first converting it into peptone ; it therefore does not liquefy 

 gelatine like the proteus ; it rapidly decomposes albumen, form- 

 ing indol and allied bodies, and even ammonia. 



Bacteria causing Ammoniacal Fermentation of Urea. 



In connection with these true putrefactive bacteria I have to 

 mention a group of bacteria which, though not strictly connected 

 with decomposition ofalbuminous matter, play an important part, 

 inasmuch as their action supplements that of the former, the 

 group in question consisting of species which can change urea 

 and allied substances into ammonium carbonate. This action 

 is generally and justly considered of the nature of a ferment or 

 hydrating action, like that of other organised ferments to be 

 presently described. But we mention this group here because 

 by changing urea into ammonium carbonate it prepares, 

 in one sense, the way for the action of certain other bacteria 

 which, by oxidising ammonia into nitrites and nitrates, are the 

 direct food-providers for the vegetable kingdom. Urea and 

 allied substances, as stated above, are the last products of 

 albuminous metabolism in man and animals, and therefore form 

 an integral part of the material destined for the soil in which 

 the plants of our gardens and fields live and thrive. I show you 

 here one of the species of this group — for there are several — the 

 micrococcus urcte ; this is a coccus growing as a white staphylo- 

 coccus, and forming connected masses in the natural or artificial 

 culture media ; it does not liquefy gelatine, grows extremely 

 rapidly at higher temperatures. 



The photographs give you an idea of the character of this 

 organism in plate, in stre.^k- and stab culture, and in micro- 

 scopic specimens ; in these latter you notice that neither in size, 

 nor arrangement, nor mode of division does this microbe show 

 anything that would distinguish it from other species of staphy- 

 lococcus ; its action on urea being its chief distinguishing 

 character, being capable of converting it into ammonium car- 

 bonate. 



At present it is well established that nitrogenous principles like 

 indol, phenol, and ammonia are produced during the decomposi- 

 tion of albumen by proteus, bacillus coli, and other putrefactive 

 bacteria ; and, further, that substances, as indol, phenol, and the 

 like, are, by the activity of certain other bacteria not yet suffi- 

 ciently investigated, converted into ammonia. We have now traced 

 the decomposition of albumen down to ammonia, and in this 

 condition it is subjected in the soil to the action of the nitrify- 

 ing bacteria — that is, bacteria which oxidise ammonia and con- 

 vert it into nitrites and ultimately into nitrates; these bacteria 

 complete then the series of processes by which the nitrogen 

 ultimately returns from where it started. It started as nitrates 

 in the soil surrounding the roots of plants, and as nitrates it 

 ultimately again finds itself in the soil ; first it had been used by 

 the plant in order to build up its albumen, then as vegetable 

 albumen it represents the food of animals ; in these it serves to 

 build up the protoplasm of the animal body, from which it 

 passes as food for carnivorous animals. The albumen of animals 

 or plants becomes decomposed by putrefactive bacteria, the 

 ultimate products of this, ammonia, becoming converted by the 

 nitrifying bacteria of the soil into nitrites and finally into nitrates. 

 " From earth to earth " expresses the beginning and end of this 

 wonderful migration and change I 



■ Nitrifying Bacteria, 

 Schlresing and Muntz were the first to show that the con- 

 version of ammonia into nitrates in the soil is most probably 

 caused by micro-organisms, but not till the researches of War- 

 ington, Winogradski, and P. Frankland, were these micro- 



NO. 1230, VOL. 48] 



organisms isolated and more carefully experimented with. 

 Warington, and particularly Winogradski, have shown that 

 there are two species of bacteria which play an important part 

 in these processes, one species converting ammonia into nitrites, 

 the other these finally into nitrates. I show you here some 

 lantern slides of Winogradski, in which these two species are 

 well shown ; the slides are of preparations of artificial cultiva- 

 tions, in which Winogradski has been extremely successful. 

 These two species (the nitrous and the nitric organism) are 

 minute rod-shaped or oval bacteria ; when in the act of dividing, 

 they form short dumb-bells ; the nitrous organism is larger than 

 the nitric, but both show forms which possess celia, and which 

 therefore are possessed of motility. Winogradski has by artifi- 

 cial cultivations obtained both these species in large quantities, 

 and, on testing them on liquids of 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 nitrify- 

 ing microbes, so important for agriculture, must be considered 

 as solved. 



Bacteria of Leguminosa. 



I have now to introduce to your notice a group of 

 organisms which, like the former, are of interest and import- 

 ance to the vegetable kingdom, at any rate to one portion of it, 

 viz. the plants belonging to the leguminosa;. 



Hellriegel and Wilfarth had shown that the excess of nitro- 

 gen in leguminosoe is obtained from the atmosphere by the 

 instrumentality 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 nitrogen can take place, and the growth of the 

 leguminous plant remains appreciably attenuated. The roots 

 ol 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 Prof. 

 Marshall Ward, of Sir John Lawes and Dr. Gilbert, of Beyer- 

 inck, Prazmowski, Nobbe, and Frank. Beyerinck, then Praz- 

 mowski, and particularly Nobbe, have shown that the nodules on 

 the roots owe their origin to the growth in the tissues of the 

 rootof certain bacteria, and it is these bacteria which are in- 

 strumental in fixing the free nitrogen. These bacteria repre- 

 sent well-defined species, and, as Nobbe has shown, difTer for 

 the different leguminoste. 



My friend Prof. Marshall Ward has been kind enough to 

 supply me for examination with roots of lupines containing the 

 nodules, and I show you here some photos as the result of this 

 examination, illustrating the distribution in the tissue of the 

 nodules 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 

 fiuorescent 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 these 

 photographs. 



Chromogenic and Phosphorescent Bacteria. 



Time does not permit of more than a passing allusion to 

 those remarkable species of chromogenic bacteria which have 

 the power to produce pigments, either pigments which become 

 dissolved in the medium in which these bacteria grow,or remain 

 limited to the substance of the bacteria themselves. Species 

 of bacteria there are which produce pigments of scarlet 

 red, orange, yellow, yellow-green, green, greenish-blue, blue, 

 violet, or pink colour. The nature of these pigments and the 

 meaning and object of their formation are still shrouded in a 

 good deal of mystery, though Erdmann and Schiotter 

 showed long ago that many points of similarity exist be- 

 tween some of these pigments and certain anilin colours. I 

 show you here cultivations of some of those chromogenic bac- 

 teria, and in a diagram the spectrum of one species, viz. of the 

 Bacillus frodigiosus ; this is the more common of the chromo- 

 genic bacteria, being occasionally present in water and in air. 

 The pigment is soluble in alcohol, though only to a limited 



