September i, 1882.] 



THE TROPICAL AGRICULTURIST. 



205 



GERMS AND BACTERIA. 



The part formerly played by electricity seems now 

 likely to be assigned to Bacteria. A few years ago, 

 when any new or strange phenomenon was made 

 known, a ready explanation was found in the word 

 electricity, and most people of an nnscientifio turn 

 of mind complacently went on their way without 

 giving a longer thouglit to the m.itter. Now-a-days 

 "Germs" and Bacteria are accepted by many as the 

 causes of various phenomena with iust as little real 

 en(iuiry. It is not that electricity is really any less 

 potent than before, Irat the potency of Bacteiua is a 

 new revelation. Although the word is getting com- 

 mon, and the effects more and more recognised,, tlie 

 detinition of Bacteria is not yet settled, their place 

 in organised Nature not known beyond dispute, then' 

 life-history l)y no means fully nnr.ivelled. It must 

 sulHce for us here to remind the reader that these 

 Bacteri.^ are, in all probabilitj', plants ; they are cert- 

 ainly of extreme minuteness, and of extreme simplicity 

 of structure, and they are probably mere transitory 

 stages of some more jjerfect organism. Under certain 

 circumstances they exist in prodigious numbers, ami, 

 under certain cii-oumstances, they bruig about changes 

 and diseases in the unfortunate anim.i,ls or plants into 

 wliich they gam an introduction. It is natural to 

 suppose that these minute gerais are but tlie accom- 

 paniments of fermentation and putrefaction — efieots, 

 not causes, and this may be so in some instances. 

 In other cases it has been proved to demonstration 

 that certaui changes and diseased conditions arise when 

 they are introduced, and do not arise when by various 

 means their entrance is prevented, or tlieir activity 

 destroyed. By experiments on animals, amongst other 

 means, these facts have been established, and not 

 only this, the means of prevention have been found. 

 One hundred and fifty thousand horses, cattle, and 

 sheep have now been vaccmated by M. Pasteur and 

 his disciples, and the success m preventmg tlie access 

 of splenic fever, if not absolute, is yet so large as 

 amply to prove the greatness of the benefit conferred. 

 As we have already referred to tliis matter, explained 

 the rationale of the process, and recorded the already 

 vast beneficial results, we need not again enter into 

 details further than to remind cultivators of fruit trees 

 tliat they have their concern in the matter, since it 

 has been asserted — though the statement requires con- 

 firmation — that a particular form of canker in Apple 

 trees Ls caused by the presence of these Bacteria. 



It is our purpose, however, now to once again call 

 attention to an aspect of the matter in which cultiv- 

 ators, whether fanners or gardeners have the deepest 

 concern — we mean the existence of these agents in the 

 soil and the work they do in it. In some romarlis 

 contributed to these columns under the title ISorce 

 Ilortidame it was shown by the writer how the differ- 

 ence between the inert " dead soil " and the " live 

 soil " might he accounted for by the presence of these 

 wonder-working agents in the one and then- absence 

 in the latter. .Sterile poor soil may and often does 

 owe its sterility, not to any real deficiency of plant 

 foo<l in the soil, but to the absence of those go-betweens 

 whose office it is to convert the msoluble to the solu- 

 ble, the useless to the useful. The food may exist in 

 abimdauce. but for want of proper cooks it may be 

 of no avail to the hungry plants. The actual quant- 

 ities of certain ingi-edients taken from the soil by 

 plants are often so small that it rarely happens that 

 a soil does not prove on analysis to contain ten times 

 — a thousand tunes — more than wliat would be required 

 for the plants growing upon it. The analysis of a soil 

 by a cliemist is, however, one thing, the analysis of 

 the same soil by a plant is quite another. Most soils, 

 for instance, contain as much potash as the plant is 

 likely to require, and yet it is not always yielded up 

 to the plant in sufficient quantities, as is proved by 



the beneficial results of the application of potash man- 

 ures. We do not yet know whether Bacteria play 

 any part m the supply of potasli in an available fonn, 

 but quite apart from potash it is certain that we 

 often actually pay for large quantities of fertilisers 

 when there is a more than sufficient supply already in 

 the soil could wc but make them available. We do 

 not la,y this down as absolute truth, of universal ap- 

 plication at all times and seasons : we are far too 

 ignorant as yet to deal in dogmas ; still what we have 

 said is, we believe, substantially a correct illustration 

 of a general truth, and represents, so far as it goes, 

 the present state of science on this matter. 



The latest publications on the subject are those of 

 Mr. Warington, who lately addressed the Society of 

 Arts on the subject. Nitre, or saltpetre— in chemical 

 language potassic nitrate, or nitrate of potash — is, as 

 has long been known, formed in the soil ui large 

 quantities in certain hot countries, and it was ascert- 

 ained by chemists that this production of potassic 

 nitrate was due to the combination of nitric acid and 

 l^otosh. The niti-ic acid necessary to form the com- 

 bination does not exist ready-made in the soil, but 

 is derived from ammonia. Now, when oxygen is added 

 to ammonia (a compound of hydrogen and nitrogen) 

 the ammonia is oxidised, as it is said, and the am- 

 monia becomes converted into nitric acid. Thus much 

 was known for certain, but until the last few ycai's 

 it was not known what brought about the oxidation 

 of the ammonia. Two French chemists, MM. Schlce- 

 siug and Mnntz, in 1877, proved that the formation 

 of nitre in the soil was due to the action of a living 

 ferment. Mr. Warington investigated the subject 

 for himself in Mr. Lawes' Laljoratory at Rothara- 

 sted, and has been enabled to confirm fully the theory 

 just mentioned, and the proof was afforded by the 

 same means as those we have before alluded to. When 

 access of germs was prevented, no nitrification took 

 place ; when they were allowed ingress, or when they 

 were _ purposely added, then the process began : so 

 that in the inorganic lifeless soil, as well as in the 

 organic living plant or animal, these humble organisms 

 play a part of first-rate importance. Mr. Warington 

 having succeeded in producing nitrification at will, 

 proceeds to show how the process may be carried on 

 on a large scale for commercial purposes ; and a per- 

 usal of his paper among other things suggests the 

 possibility of making our own nitrate of soda, and of 

 thus reducing the cost of this valuable manure. 



Another very important aspect of the case is touched 

 on by Mr. Warington ; we allude to the purification 

 of sewage. The purification of sewage by the soil 

 depends upon one or more of the following causes ; — 

 1, simple filtration ; 2, on the precipitation and reten- 

 tion by the soil of ammonia, &c., previously m solu- 

 tion ; and lastly, and especially, by the oxidation of 

 the anunonia and of organic matter by the agency of 

 living organisms (Bacteria). These organisms are 

 abundantly present in surface soils, but are probably 

 absent, or nearly so, from sub-soils, but sewage and 

 farmyard manure contain the organisms necessary for 

 their own destruction, and the supply of the plant 

 with food. The amount of nitrates formed in tlie soil, 

 and which are so important to plants — inasmuch as 

 it is through them that vegetation derives its nitro- 

 gen — is very large, and has formed the subject of 

 special investigation at Rothamsted. There the rain- 

 fall, the amount of drainage water per acre, do\m to 

 a depth of 60 inches, and the quantity of nitrogen 

 in that water have been detennined for the last five 

 years, the general result being that nitrates are seen 

 to be produced in large quantities even in uinnaiun-ed 

 fallow soil, more especially in the hot autumn mouths ; 

 on the other hand, during tUa rainy months a large 

 quantity of the nitrates will be washed away, to the 

 detriment of the soil's fertility. The gi-owtli of any 



