58o 



NATURE 



\Oct. lo, 1889 



changes which they alone can bring about at once begin. A few 

 cells of the yeast plant set up the vinous fermentation in a sugar 

 solution. This is clearly stated by Pasteur as follows: — "My 

 decided opinion," he says, "on the nature of alcoholic fermen- 

 tation is the following. The chemical act of fermentation is 

 essentially a correlative phenomenon of a vital act beginning and 

 ending with it. I think that there is never any alcoholic fer- 

 mentation without there being at the same time organization, 

 development, multiplication of globules, or the continued 

 consecutive life of globules already formed." 



Add on a needle's point a trace of the peculiar growth which 

 accompanies the acetous fermentation, and the sound beer or 

 wine in a short time becomes vinegar. Place ever so small a 

 quantity of the organism of the lactic fermentation in your sweet 

 milk, which may have been preserved fresh for years in absence 

 of such organisms, and your milk turns sour. But still more, the 

 organism (yeast) which brings about the alcoholic fermentation 

 will not give rise to the acetous, and vice vetsA, so that each 

 peculiar chemical change is brought about by the vital action of 

 a peculiar organism. In its absence the change cannot occur ; in 

 its presence only that change can take place. 



Here again we may ask, as Pasteur did, Why does beer or 

 wine become sour when exposed to ordinary air? And the 

 answer to this question was given by him in no uncertain tone 

 in one of the most remarkable and most important of modern 

 experimental researches. Milk and beer which have become 

 sour on standing in the air contain living micro-organisms which 

 did not exist in the original sound fluids. Where did these or- 

 ganisms originate ? Are they or their germs contained in the 

 air, or are these minute beings formed by a process of spon- 

 taneous generation from material not endowed with life ? 



A controversy as to the truth or falsity of the theory of spon- 

 taneous generation was waged with spirit on both sides, but in 

 the end Pasteur came off victorious, for by a series of the most 

 delicate and convincing of experiments he proved the existence 

 of micro- organic forms and their spores — or seeds — in the air, 

 and showed that whilst unpuiified air was capable of setting up 

 fermentative changes of various kinds, the same air freed from 

 germs could not give rise to these changes. Keep away the special 

 germ which is the incentive to the pathological change, and that 

 change cannot occur. In the interior of the grape, in the healthy 

 blood, no such organisms, no such germs exist ; puncture the 

 grape or wound the animal body, and the germs floating in the 

 air settle on the grape-juice or on the wounded tissue, and the 

 processes of change, whether fermentative or putrefactive, set in 

 with all their attendant symptoms. But crush the grape or 

 wound the animal under conditions which either preclude the 

 presence or destroy the life of the floating germ, and again no 

 such change occurs ; the grape-juice remains sweet, the wound 

 clean, 



I have said that every peculiar fermentative change is accom- 

 panied by the presence of a special ferment. This most im- 

 portant conclusion has only been arrived at as the result of 

 careful experimental inquiry. How was this effected? By the 

 artificial cultivation of these organisms. Just as the botanist or 

 gardener picks out from a multitude of wild plants the special 

 one which he wishes to propagate, and planting it in ground 

 favourable to its growth, obtains fresh crops of the special plant 

 he has chosen, so the bacteriologist can by a careful process of 

 selection obtain what is termed a pure cultivation of any desired 

 organism. Having obtained such a pure cultivation, the next 

 step is to ascertain what are the distinctive properties of that 

 special organism ; what characteristic changes does it bring about 

 in material suitable for its growth. This having been determined, 

 and a foundation for the science having thus been laid, it is 

 not difficult lo apply these principles to practice, and the first 

 application made by Pasteur was to the study of the diseases of 

 beer and wine. 



In September 1871, Pasteur visited one of the large London 

 breweries, in which the use of the microscope was then unknown. 

 A single glance at the condition of the yeast instantly told its 

 tale, and enabled him to explain to the brewers the cause of the 

 serious state of things by which frequently as much as 20 per 

 cent, of their product was returned on their hands as unsaleable 

 — this being that this yeast contained foreign or unhealthy or- 

 ganisms. And just as pure yeast is the cause of the necessary 

 conversion of wort into beer, so these strange forms which 

 differ morphologically from yeast, and whose presence can 

 therefore be distinctly ascertained, are the cause of acidity, 

 ropiness, turbidity, and other diseases which render the 



beer undrinkable. It is no exaggeration to say that, whereas- 

 before Pasteur's researches the microscope was practically 

 unknown in the brewhouse, it has now become as common 

 as the thermometer or the saccharimeter, and by its help and 

 by the interpretations we can place upon its revelations through 

 Pasteur's teaching, yeast — of all brewers' materials the least open 

 to rough and ready practical discernment — becomes easy of 

 valuation as to ils purity or impurity, its vigour or weakness, 

 and, therefore, its behaviour during fermentation. Thus, while, 

 in former days the most costly materials were ever liable to be 

 ruined by disease organisms unconsciously introduced into them 

 with the yeast, at the present day the possibilities of any such 

 vast pecuniary disasters become easily avertable. 



Of all industries, brewing is perhaps the one which demands 

 the most stringent care in regard to complete and absolute 

 cleanliness. The brewers' materials, products, and by-products, 

 are so putrescible, there is always so vast an abundance of dis- 

 ease-organisms in the brewery air, that the minutest amounts of 

 these waste products lying about in vessels or pipes transform, 

 these places into perfect nests for the propagation of these micro- 

 organisms, whence, transferred into the brewings, they inevitably 

 ruin them, however carefully and scientifically prepared in other 

 respects. Without the microscope, any breach of discipline in 

 the way of the supreme cleanliness necessary is impossible of 

 detection ; with it we can track down the micro-organisms to 

 their source, whether it be in uncleanly plant, in impurity of 

 materials, or in carelessness of manipulation. 



Among the more direct applications of Pasteur's researches, 

 the so-called Pasteurization of beer claims a place. Pasteur 

 showed that temperatures well below the boiling-point sufficed 

 for destroying the disease organisms in alcoholic fluids, and, 

 based on these results, enormous quantities of low-fermentation 

 beers are annually submitted to these temperatuies, and thus- 

 escape the changes otherwise incident to the micro-organisms 

 which have succumbed to the treatment. This process is, how- 

 ever, for several intricate reasons, not suited for English beers, 

 but if we cannot keep our beers by submitting them to high 

 temperatures, we can foretell to a nicety how they will keep by 

 artificially forcing on those changes which would occur more 

 slowly during storage. The application of a suitable tempera- 

 ture, the exclusion of outside contamination, a microscopic 

 examination of the "forced" beer, and the knowledge which 

 we owe to Pasteur of what the microscopic aspect means, 

 sufifice to make each brewing foretell its own future history, and 

 thus suffice to avert the otherwise inevitable risks incident to the 

 storage and export of beer, the stability of which is unknown. 



Brewing has thus become a series of precise and definite 

 operations, capable of control at every point. Instead of de- 

 pending — as it had to depend — on intuition and experience 

 handed down in secrecy from father to son, it now depends upon 

 care, forethought, and the soundness of the brewer's scientific 

 training. This change in the nature of the brewer's operations, 

 and in the persons who govern them, is primarily due to Pasteur. 

 Other men have done much to carry on his work, but it is to his 

 example of ceaseless patience, and to his example of freely pub- 

 lishing to the world all the results of his work, that the brewers 

 of all countries are indebted for the connection of each pheno- 

 menon with a controllable cause, and for thus emancipating 

 their industry from empiricism and quackery. 



Much the same story has to be told about Pasteur's investiga- 

 tion of wine and its diseases. As with the brewer, so with the 

 wine-grower Pasteur has pointed out the causes of his troubles, 

 and, the causes having been ascertained, the remedies soon fol- 

 lowed, and the practical value of these researches to the trade 

 of France and other wine-producing countries has been 

 enormous. 



The next labour of our scientific Hercules was of a different 

 kind, but of a no less interesting or important character. The 

 south of France is a great silk-producing district. In 1853 the 

 value of the raw silk was represented by a sum of some five 

 millions sterling, and up to that date the revenue from this source 

 had been greatly augmenting. Suddenly this tide of prosperity 

 turned, a teiTible plague broke out amongst the silkworms, and 

 in 1865 so general had the disease become that the total 

 production of French silk did not reach one million, and the 

 consequent poverty and suffering endured in these provinces 

 became appalling. Every conceivable means was tried to over- 

 come the disease, but all in vain. The population and the 

 Government of France — for the evil was a national one — were 

 at their wits' end, and a complete collapse of one of the most 



