1^.6 



NA TV RE 



[June 9, 1892 



author of prose. It was Pasteur also who first infused science 

 into the operations of the wine-vat and the fermenting-tun, by 

 his classical " Etudes sur la Biere et sur le Vin." It was he who 

 first showed that the normal work of the brewery was accom- 

 plished by particular forms of micro-organisms, known as yeast, 

 and that the frequent failures to produce beer or wine of the 

 desired quality was occasioned by the presence of foreign forms 

 of micro-organisms giving rise to acidity and other undesirable 

 changes in these beverages. 



In these researches of Pasteur's on beer and wine, we are 

 almost for the first time brought face to face with the precise 

 nature of some of the ch-mical changes which micro-organisms 

 bring about. The time-honoured vinous fermentation of sugar, 

 the products of which had been valued and indulged in by man 

 even from the days of Noah, is for the first time so accurately 

 studied as to be definable almost with the precision of a chemical 

 equation. 



Similar attention was also given by Pasteur to some of the 

 other microorganisms which deteriorate the quality of the beer — 

 thus more especially to the bacterium which causes the acetic or 

 vinegar fermeniation, which is a process oi oxidation, transform- 

 ing alcohol into vinegar ; to the bacillus inducing the tactic 

 fermentation, which is a process of decomposition, in which sugar 

 yields lactic acid ; as well as to that which brings about the 

 butyric {txxatx\\.zX\o\\, a. [)rocQ>s of reduction, in which butyric acid 

 is formed. 



These are the foundations and scafiblding on which subsequent 

 investigators of the phenomena of fermentation have laboured. 

 Thus, making use of more refined methods than those which were 

 at the disposal of Pasteur, Christian Hansen, of Copenhagen, 

 has enormously extended our knowledge of the alcohol-pcoducing 

 organisms or yeasts ; he has shown that there are a number of 

 distinct forms, differing indeed but little amongst themselves in 

 shape, but possessing very distinct properties, more especially in 

 respect of the nature of certain minute quantities of secondary 

 products to which they give rise, and which are highly important 

 as giving particular characters to the beers produced. Hansen 

 has shown how these various kinds of yeast may be grown or 

 cultivated in a state of purity even on the industrial scale, and 

 has in this manner revolutionized the practice of brewing on the 

 Continent. For during the past few years these pure yeasts, 

 each endowed with particular qualities, have been grown with 

 scrupulous care in laboratories equipped expressly for this pur- 

 pose, and these pure growths are thence despatched to breweries 

 in all parts of the world, particular yeasts being provided for the 

 production of particular varieties of beer. In this manner 

 scientific accuracy and the certainty of success are introduced 

 into an industry in which before much was a matter of chance, 

 and in which nearly everything was subordinated to tradition and 

 blind empiricism. 



T/ie Bacteria connected with the Soil. 



It is, however, with regard to the bacteria connected with 

 other industries than those of alcoholic feimentation that our 

 knowledge has particularly advanced during the last few years. 

 Thus some of the most important phenomena in agriculture 

 have recently received a most remarkable elucidation through 

 the study of bacteria. 



Scientific agriculturists are generally agreed that one of the 

 most important plant-foods in the soil is nitric acid; indeed they 

 inform us that if a soil were utterly destitute of this material it 

 would be incapable of growing the barest pretence of a crop, 

 either of corn, or of roots, or of grass, even if the soil were in 

 other respects of the most superb texture, however favourably it 

 might be situated, however well drained, tilled, and supplied 

 with the purely mineral ingredients of plant-food, such as 

 potash, lime, and phosphoric acid. 



Yet, notwithstanding the commanding importance of this 

 substance nitric acid to vegetation, it is present in ordinary 

 fertile soils in but little more than homoeopathic doses. 



These facts are gathered from those grand experiments which 

 have during the past half-century been going on at Rothamsted 

 under the direction of Sir John Lawes and Dr. Gilbert, and 

 which have rendered the Hertfordshire farm a luminous centre 

 of the whole agricultural world. 



From these experiments it appears that sometimes there is in 

 fertile soil under i part, and often under lo parts, of nitrogen as 

 nitrate per million of soil. 



Indeed, in order to detect and estimate these minute 

 quantities, the most refined methods of chemical analysis have 



NO. II 80, VOL. 46] 



to be called into requisition. [Demonstration of the presence of 

 nitric acid in soil by diphenylamine test.] 



Now the cause of .such minute quantities only of nitric acid 

 being found in soils is due partly to this material being washed 

 away by the rain, and partly to its being so eagerly taken up by 

 plants for the purposes of nutrition ; for it has long been known 

 that by ."-uitable means the quantity can be enormously increased 

 if no vegetation is maintained, and the ground properly pro- 

 tected from lain. The soil, in fact, under ordinary circum- 

 stances, continuously generates this nitric acid from the various 

 nitrogenous manures which are applied to it, and it is in the 

 form of nitric acid that the nitrogen of manures principally 

 gains access as nutriment to the plant. 



It was in the year 1877 that two French chemists, Schloesing 

 and Miintz, showed that this power of soils to convert the 

 nitrogen of nitrogenous substances into nitric acid was due to low 

 forms of life — to micro-organisms or bacteria. The proof which 

 they furnished of this statement was of a very simple character, 

 and consisted essentially in demonstrating that this production 

 of nitric acid, or process of nitrification, as it is generally called, 

 is promptly inhibited or brought to a standstill by all those 

 materials which have the property of destroying micro-organisms, 

 and which we call antiseptics ; whilst similarly the process is 

 stopped by heat and other influences which are known to be 

 fatal to Hfe in general. 



These results of Schlcssing and Miintz were confirmed and 

 greatly extended in this country by Mr. Warington and Dr. 

 Munro, but although the vital nature of the process was fully 

 established, little practical advance was until recently made in 

 the identification or isolation of the particular bacteria respon- 

 sible for this remarkable and invaluable transformation. 



In 1886, however, a very important step was made by Dr. 

 Munro, who showed that this process of nitrification could take 

 place in solutions practically destitute of organic matter, or, in 

 other words, that the vital activity of the bacteria of nitrification 

 could be maintained without nutriment of an organic nature. 



In 1885, I had myself already established the fact that some 

 micro-organisms can actually undergo enormous multiplication 

 in ordinary distilled water : — 



Multiplication of Micro-organisms in Distilled Water. "^ 



Hours after introduction 

 of micro-organisms. 



O 



6 



24 



48 



In taking up the subject of nitrification in conjunction with 

 my wife in the autumn of 1886, I determined to avail myself of 

 this remarkable property of the nitrifying organisms to grow in 

 the absence of organic matter, thinking that in this way it would 

 be possible to achieve a separation of the nitrifying organisms 

 fiom other forms which can only grow if organic food materials 

 are supplied to them, 



Proceeding on these lines, we have carried on the process of 

 nitrification over a period of upwards of four years without the 

 nitrifying organisms being supplied with any organic food 

 materials whatsoever : — 



Compositiiu of Solution employed for Nitrification. 



Ammonium chloride '5 grm.^i 



Potassium phosphate ... "i 



Magnesium sulphate... ... "02 



Calcium chloride ... ... *oi 



Calcium carbonate .. ... 5"0 



Number of micro-organisms 

 found in i c.c. of water. 

 ... 1,073 

 ... 6,028 

 7,262 



[ In 1000 c.c. of 

 { distilled water. 



In a solution of this composition the process of nitrification 

 was carried on over a period of upwards of four years, as indi- 

 cated in the table on p. 137. 



In carrying on this series of experiments it was soon evident 

 that although a number of forms foreign to the nitrification pro- 

 cess were being eliminated, there were still some remaining 

 alongsideof the nitrifying organisms, or, in other words, that a 

 pure culture of the nitrifying organisms had not been obtained. 

 From various considerations, however, we came to the con- 

 clusion that the nitrifying organisms probably differed from the 

 other forms which were still present along with them in being 

 unable to grow on the common cultivating medium employed by 

 bacteriologists, and known as gelatin-peptone. 



1 Proc. Roy. Soc, i88 



