SCIENTIFIC.

Otago Witness, Issue 1928, 2 November 1888, Page 35

SCIENTIFIC.

M. LOUIS PASTEUR.

HIS LIFE AND RESEARCHES. (By Hebbbbt O. Barclay, Otago University.) ll.— Fermentation. It is in fltudying these little creatures— the microbes or germs — that Pasteur has spent the greater part of his life. At the age of 33 years he was elected Dean of the Facnlte dcs Sciences at Lille. In this district the manufacture of alcohol from beetroot is an important industry, and Pasteur's interest in micro-organisms having been awakened he was led 1 , into the study of fermentation. At that time Fabroni held that fermentation was merely a chemical process. Gay-Lussac thought that the' presence of oxygen of the atmosphere was the determining cause of fermentation. Caiquard-Latour, and Schwann discovered the | composition of yeast at the same time, and they referred' the process to the action of the plantlike celte. This was & distinct advance on the theories, of previous scientists, but the theory , wanted proving. Spallanzani demonstrated the possibility of stopping fermentative or putrefactive chapge by boiling the putrescible substance to kill the germs present in it, and then hermetically sdaling the mouths of the bottles, by this means preventing the access of organisms from outside. Schulze then showed that the orga-' nisms are derived from the air, and do not arise spontaneously in liquids, and he introduced the method of "sterilising" air — or rendering it free from germs— bypassing it over a very hot platinum p|ate. This process destroys the. microorganisms floating in the air by burning them up together with all other organic matter present. Schroeder then pointed out another method for sterilising air — viz., by passing it through -cotton wool. While these discoveries were beiog made the great scientific authority of his djiy — Liebig — had withheld his support from the doctrine that was rapidly gaining ground. He maintained " that putrefaction was the ! result of the combustion of one or more elements of the organic substances at the expense of their own oxygen " — i c., they used up their iown oxygen when oxygen of the air was excluded ; and he said that substances that did not undergo these changes spontaneously needed to be brought into contact with substances that were putrefying, and this substance was the ferment — eg., yeast in the sugar fermentation. The problem was in this unsettled con- ! dition when Pasteur took the subject up. His first' crucial experiment was the one by \ which he demonstrated that the yeast cells ' could live in a fluid made up of salts only, ; and he ' prepared a solution which still bears his! name.' The yeast cells could split up thesalts, which contained all the essentials of their food, anq rebuild again the complex - organic molecule from these elements ; they could make albumen ifrom simple unorganised matter. Thi9 is a capacity that higher organisms are deprived of. They need albumen already prepared as part of their fqod, and it is taken in the form of meat, eggs, vegetables, &o. Plants like the yeast; cellshave this, power, they bnild up their albumen from salts taken from the soil and from gases contained^ in ihe atmosphere which they absorb. In the presence of sugar the yeast cells break up the salts in the solution, and in addition to that they decompose or .break down the sugar^and take a portion of it for their own nutrition.. That is to say, Liebig's theory of mere,. contact did not hold good. .The processes of change taking place in the ferment did not communic ite a tendency to change in the sugar merely, be muse' the two were placed side by side, but the f e: 'ment actually decomposed the sugar, ! aridinthii decomposition alcohol, carbonic acid, : glycerine, pnd succinic acid were formed. Pas- \ teur had discovered' the real bond— the real link | —which explained the necessity for the presence of yeast cells in the alcoholic fermentation, and j he, had explained the true jpart thatf the yeast plant play^in^e.mWr-^tidgprbiiefla: Ftetelir then inquired into otSer nlstances f dFferihentj!i-, tive change. The soaring of -'niillcisfaootier 1 example. sln this case lactose, or sugar of- milk, becomes ttansfdrined/mto lactic acid, and this may underfed i a furthetf change, ihe lactic acid being converged in,to butyrio'acid. In each case Pasteur ,d: sco veaed. a small organism as the cause of. .tt c change. In the case of the butyric *cid fernu atation the great investigator found that the yi nios which caused the change could live witboti t cpataot with the aife-&&, without oxygen ; hi fact the presence of oxygen killed t^ei^wftili ths othex wganiama he had conad

across did live in the presence of oxygen. Hence Pasteur classified these organisms into Anzerobes, those that could live without air ; and Aerobes, those that live in the presence of air. Furtherpursuinghisinvestigatione, he asked, Why did the cells of the yeast plant" break up the sugar? He thought he saw why, and then he experimented to see if his supposition was rights Id the large vats that brewers i use the heavy carbonic acid lies on the surface of the liquid and prevents the access of oxygen. Pasteur placed a number of very shallow pans with the fermenting fluid in them to the air, and the result was rapid fermentation— but with I what result ? While in the deep vats one kilo of ferment could split up 70 to 15(hkilos of sugar, in the shallow pans one kilo of' ferment could ' effect change in some five or six kilos only of sugar. The explanation he offered of the phenomenon was this : that if the fermenb was exposed to atmospheric air it fed most easily on the oxygen contained therein, while if it was closod off from the air — as by a thick layer of carbonic acid gas— it has to seek for oxygen in another direction, and the easiest; method of obtaining it is by splitting up the sugar and taking. its oxygen, and in this change the byes products— alcohol, &o.— are formed. Of the sugar thus split into pieces 95 per cent, formalcohol and carbonic acid, 4 per cent, becomes glycerine and sucoinic acid, and 1 per cent, is taken as food by the yeast. The result of Pasteur's investigations on fermentation proved that .the air was full of organisms or their 'spores, arid that in a suitable medium they were always ready to develop and multiply with great rapidity, and there they set up putrefactive or fermentative changes, for the two processes are exactly similar, the only difference being that bad smelling gases are evolved in the former case. Conversely, if air or liquids containing such organisms be kept away from or purified before admission to putrescible material, then putrefaction will not occur. This great discovery—worked up by Pasteur's predecessors, and ultimately proved by himself— lies at the foundation of other discoveries in similar directions, and on this principle the whole of the antiseptic treatment in surgery is based. Spontaneous Generation. Into the great dispute of the day—spontaneous generation— Pasteur was imperceptibly led. By his friends ho was urged not to waste his time in such an unprofitable field. Liebig, the great authority, sided with the doctrine—* viz., that life could arise otherwise than from [ pre-existing life— that is, practically, that life could arise from dead matter. The problem to be solved could be solved only in [ one way— namely, by keeping out from a fluid in which organisms could exist all contamination from outside sources, having ■ pre- ! viously sterilised the fluid. If all experiment showed that it was only by means of contamination by living orgnnisms that life arose in the liquid, then the negative was proved, so far as I it could be, that life could not arise otherwise than from pre-existing life. If the upholders of the cloctrifte showed that they had eliminated all chances of contamination and yet life had arisen, it was the duty of the opposing party to prove that the experiments were badly oarried ' out, and that nil means of access of germs from without were not guarded against. When Pasteur went into the question M. Pouchet was leading the upholders of the doctrine, and be had to 'meet the subtle arguments of thai inquirer, and he was not long before he succeeded in demonstrating before the Academy of Sciences a blunder Pouchet had made in carrying o"ut one" of his famous experiments. Pouchet having boiled a bottle of water, turned it upside down under mercury, and then admitted pure oxygen to it, and after that he added a bundle of hay which ■- had been kept in a hot chamber at lQOdeg fbr some time previously to sterilise it. In eight days organisms appeared. They must have come by spontaneous generation, said Pouchet. Not at all, said Pasteur ; and before a meeting of the Academy he succeeded in completely upsetting Pouchet's contention by proving that the mercury — not being sterilised j — was the source of the impurity. I Pasteur then proceeded to prove the existence '", I of spores in the atmosphere by examining, microscopically, air which had been filtered - through cottonwool, and he succeeded admirably. Oneof hisinostinterestingexperiments was the following, and it has been somewhat improved on by Tyndall. In a flask he boiled some yeast water and then during ebullition he drew the neck out to a considerable length and then he bent it, but the tube, though having a very fine bore, was nob closed to the air. Now, notwithstanding that the outside impure air was admitted into the interior of the flask, still no development of life occurred. Air Lifter had in his possession such a flask for 13 years in which no trace oL putrefaction was visible. The reason is this — that dust-laden air passing along the bend of the tube very slowly deposits by gravitation tho germs, and they never reach the fluid. Violent shakes of the bottle, or the passage of a small quantity of water from the flask into the tube and then back into the bottle, upsets the whole experiment. Professor TyndalPs researches have since corroborated this view. By examining air with a strong beam of an electric light he finds it laden with floating matter and dust of all sorts, and he states that as the result of gravitation acting on a perfectly still atmosphere for some time the air gets quite purified. Pasteur also established the fact that the number of germ.? vary in the atmosphere, whether the air be that of the town or the country,, being' far impurcr in the former situation and in lowlying places, while high mountain air is comparatively pure. Competing for a prize offered by the Academy of Sciences for an elucidation of this Subject, Pasteur completely worsted Pouchet — in fact the latter ultimately backed out of the contest altogether. The question now ia almost settled, and only a few scientists at the present 'day 1 hold .that life can arise otherwise than from, pre-existing, life, and among these is Dr Bastian. M. Pouchet is of opinion that animals even'tothe size of fleas arise spontaneously, but I know of no on,e who would support such a chimera of Aristotelian origin. At one time animals tfer'e supposed to be formed from the mud of, the Nile .by the action of the sun's 'rays. ' Aristofte^ said' fishes were made from the sea, and that^brno insects grew from the dew whw& : falls- on : plants'. Such myths.,? are -no* put- asJde^ and to. . Pasteur is due most of .the credit for having carried the day in favour' of, Biogenesis, though he had many a co-worker in the same field, and .like all men had learned much from , the successes and failures of his "contemporaries .and his predecessors. - 11 <y , \ '..,.. • ' ': ' ! (To be continued;. l >'• •■■■<■

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