Oct. 30, 1884] 



NA TURE 



645 



18 inches from the Mirface has been proved to contain the nitri- 

 fying organism by the fact that it has produced nitrification in 

 the solutions to which it was added ; while in twelve distinct 

 experiments made with soil from greater depths no nitrification 

 has yet occurred, and we must therefore conclude that the nitri- 

 fying organism was not present in the samples of soil taken. 

 The third series of experiments has continued as yet but three 

 months and a half; at present no nitrification has occurred with 

 soil taken below 9 inches from the surface. It would appear, 

 therefore, that in a clay soil the nitrifying organism is con- 

 fined to about 1 8 inches from the surface ; it is most abundant 

 in the first 6 inches. It is quite possible, however, that m 

 the channels caused by worms, or by the roots of plants, 

 the organism may occur at greater depths. In a sandy soil we 

 should expect to find the organism at a lower level than in clay, 

 but of this we have as yet no evidence. The facts here men- 

 tioned are in accordance with the microscopical observations 

 made by Koch, who states that the micro-organisms in the soils 

 he has investigated diminish rapidly in number with an increasing 

 depth ; and that at a depth of scarcely I metre the soil is almost 

 entirely free from bacteria. 



Some very prac ical conclusions may be drawn from the facts 

 now stated. It appears that the oxidation of nitrogenous matter 

 in soil will be confined to matter near the surface. The nitrates 

 found in the subsoil and in subsoil drainage waters have really 

 been produced in the upper layer of the soil, and have been 

 carried down by diffusion, or by a descending column of water. 

 Again, in arranging a filter-bed for the oxidation of sewage, it is 

 obvious that, with a heavy soil lying in its natural state of con- 

 solidation, very little will be gained by making the filter-bed of 

 considerable depth; while, if an artificial bed _ is to be con- 

 structed, it is clearly the top soil, rich in oxidising organisms, 

 which should be exclusively employed. 



The Substances susceptible of Nitrification. — The analyses of 

 soils and drainage waters have taught us that the nitrogenous 

 humic matter resulting from the decay of plants is nitrifiable ; 

 also that the various nitrogenous manures applied to land, as 

 farmyard manure, bones, fish, blood, rape-cake, and ammonium 

 salts, undergo nitrification in the soil. Illustrations of many of 

 these facts from the results obtained in the experimental fields 

 at Rothamsted, have been published by Sir J. B. Lawes, Dr. J. 

 H. Gilbert, and myself, in a recent volume of the Journal of 

 the Royal Agricultural Society of England. In the Rothamsted 

 Laboratory, experiments have also been made on the nitrification 

 of solutions of various substances. Besides solutions containing 

 ammonium salts and urea, I have succeeded in nitrifying solu- 

 tions of asparagine, milk, and rape-cake. Thus, besides am- 

 monia, two amides, and two forms of albuminoids have been 

 found susceptible of nitrification. In all cases in which amides 

 or albuminoids were employed, the formation of ammonia pre- 

 ceded the production of nitric acid. Mr. C. F. A. Tnxen has 

 already published in the present year two series of experiments 

 on the formation of ammonia and nitric acids in soils to which 

 bone-meal, fish-guano, or stable-manure had been applied ; in 

 all cases he found the formation of ammonia preceded the forma- 

 tion of nitric acid. 



As ammonia is so readily nitrifiable, we may safely assert that 

 every nitrogenous substance which yields ammonia when acted 

 on by the organisms present in soil is also nitrifiable. 



Cer ain Conditions having Great Influence on the Process of 

 Nitrification. — If we suppose that a solution containing a nitri- 

 fiable substance is supplied with the nitrifying organism, and 

 with the various food-constituents necessary for its growth and 

 activity, the rapidity of nitrification will depend on a variety of 

 circumstances : — (1) The degree of concentration of the solution 

 is important. Nitrification always commences first in the weakest 

 solution, and there is probably in the case of every solution a 

 limit of concentration beyond which nitrification is impossible. 

 (2) The temperature has great influence. Nitrification proceeds 

 far mote rapidly in summer than in winter. (3) The presence or 

 absence of light is important. Nitrification is most rapid in 

 darkness ; and in the case of solutions, exposure to strong light 

 may cause nitrification to cease altogether. (4) The presence of 

 oxygen is of course essential. A thin layer of solution will 

 nitrify sooner than a deep layer, owing to the larger proportion 

 of oxygen available. The influence of depth of fluid is most 

 conspicuous in the case of strong solutions. (5) The quantity of 

 nitrifying organism present has also a marked effect. A solu- 

 tion seeded with a very small amount of organism will for a long 

 lime exhibit no nitrification, the organism being (unlike some 



other bacteria) of very slow growth. A solution receiving an 

 abundant supply of the ferment will exhibit speedy nitrification, 

 and strong solutions may by this means be successfully nitrified, 

 which with small seedings would prove very refractory. lhe 

 speedy nitrification which occurs in soil (far more speedy than in 

 experiments in solutions under any conditions yet tried) is 

 probably owing to the great mass of nitrifying organisms which 

 soil contains, and to the thinness of the liquid layer which covers 

 the soil particles. (6) The rapidity of nitrification also depends 

 on the degree of alkalinity of the solution. Nitrification will not 

 take place in an acid solution, it is essential that some base 

 should be present with which the nitric a id may combine ; 

 when all available base is used up nitrification cea-es. It ap- 

 peared of interest to ascertain to what extent nitrification would 

 proceed in a dilute solution of urine without the addition of any 

 substance save the nitrifying ferment. As urea is converted into 

 ammonium carbonate in the first stage of the action of the fer- 

 ment a supply of salifiable base would at first be present, but 

 would gradually be consumed. The result of the experiment 

 showed that only one-half the quantity of nitric acid was formed 

 in the simple urine solution as in similar solutions containing 

 calcium and sodium carbonate. The nitrification of the urine 

 had evidently proceeded till the whole of the ammonium had 

 been changed into ammonium nitrate, and the action had 

 then ceased. This fact is of practical importance. Sewage 

 will be thoroughly nitrified only when a sulficient supply ot 

 calcium carbonate, or some other base, is available. If, instead 

 of calcium carbonate, a soluble alkaline salt is present, the 

 quantity must be small, or nitrification will be seriously hin- 

 dered. Sodium carbonate begins to have a retarding influ- 

 ence on the commencement of nitrification when its amount 

 exceeds 300 milligrammes per litre, and up to the present time I 

 have been unable to produce an effective nitrification in solutions 

 containing 1 -ooo gramme per litre. Sodium hydrogen carbonate 

 hinders far less the commencement of nitrification. Ammonium 

 carbonate, when above a certain amount, also prevents the com- 

 mencement of nitrification. The strongest solution in which 

 nitrification has at present commenced contained ammonium 

 carbonate equivalent to 368 milligrammes of nitrogen per 

 litre. This hindrance of nitrification by the presence of an 

 excess of ammonium carbonate effectually prevents the nitri- 

 fication of strong solutions of urine, in which, as already men- 

 tioned, ammonium carbonate is the first product of fermentation 

 Far stronger solutions of ammonium chloride can be nitrified 

 than of ammonium carbonate, if the solution of the former salt 

 is supplied with calcium carbonate. Nitrification has in fact 

 commenced in chloride of ammonium solutions containing more 

 than 2 grammes of nitrogen per litre. 



The details of the recent experiments, some of the results ot 

 which we have now described, will, it is hoped, shortly appear 

 in the Journal oi the Chemical Society of London. 



Harpenden, July 21 



RESEARCHES ON THE ORIGIN AND LIFE- 

 HISTORIES OF THE LEAST AND LOWEST 

 LIVING THINGS^ 



II. 



BUT the point of difficulty was B. termo. The demonstration 

 of its flagella was a task of difficulty which only patient pur- 

 pose could conquer. But by the use of our new lenses, and 

 special illumination we— my colleague and I— were enabled to 

 demonstrate clearly a flagellum at each end of this least of 

 living organisms, as you see, and by the rapid lashing of the 

 fluid, alternately or together, with these flagella, the powerful, 

 rapid, and graceful movements of this smallest known living thing 

 are accomplished. Of course these fibres are inconceivably fine 

 —indeed for this very reason it was desirable, if possible, to 

 measure it, to discover its actual thickness. We all know that, 

 both for the telescope and the microscope, beautiful apparatus 

 are made for measuring minute magnified details. Hut unfor- 

 tunately no instrument manufactured was delicate enough to 

 measure directly this fibre. If it were measured it must be 

 by an indirect process, which I accomplished thus :— The 

 diameter of the body of B. termo, i.e. from side to side, may in 

 different forms vary from the 20- to the 50-thousandth of 

 an inch. That is a measurement which we may easily make 

 directly with a micrometer. Having ascertained this, I deter- 

 • By Rev. W. H. Dallinger, LL.D., F.R.S., F.L.S.. Pres.R M S. Con- 

 tinued from p. 622. 



