a history of science-4-第44章
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eference； in ten of the remainder； through the straight tube attached to each； some drops of the washing…water were introduced； in a third series of ten flasks a few drops of the same liquid were placed after it had been boiled； and； finally； in the ten remaining flasks were placed some drops of grape…juice taken from the inside of a perfect fruit。 In order to carry out this experiment； the straight tube of each flask was drawn out into a fine and firm point in the lamp； and then curved。 This fine and closed point was filed round near the end and inserted into the grape while resting upon some hard substance。 When the point was felt to touch the support of the grape it was by a slight pressure broken off at the point file mark。 Then； if care had been taken to create a slight vacuum in the flask； a drop of the juice of the grape got into it； the filed point was withdrawn； and the aperture immediately closed in the alcohol lamp。 This decreased pressure of the atmosphere in the flask was obtained by the following means： After warming the sides of the flask either in the hands or in the lamp…flame； thus causing a small quantity of air to be driven out of the end of the curved neck； this end was closed in the lamp。 After the flask was cooled； there was a tendency to suck in the drop of grape…juice in the manner just described。
〃The drop of grape…juice which enters into the flask by this suction ordinarily remains in the curved part of the tube； so that to mix it with the must it was necessary to incline the flask so as to bring the must into contact with the juice and then replace the flask in its normal position。 The four series of comparative experiments produced the following results：
〃The first ten flasks containing the grape…must boiled in pure air did not show the production of any organism。 The grape…must could possibly remain in them for an indefinite number of years。 Those in the second series； containing the water in which the grapes had been washed separately and together； showed without exception an alcoholic fermentation which in several cases began to appear at the end of forty…eight hours when the experiment took place at ordinary summer temperature。 At the same time that the yeast appeared； in the form of white traces； which little by little united themselves in the form of a deposit on the sides of all the flasks； there were seen to form little flakes of Mycellium； often as a single fungoid growth or in combination； these fungoid growths being quite independent of the must or of any alcoholic yeast。 Often； also； the Mycoderma vini appeared after some days upon the surface of the liquid。 The Vibria and the lactic ferments properly so called did not appear on account of the nature of the liquid。
〃The third series of flasks； the washing…water in which had been previously boiled； remained unchanged； as in the first series。 Those of the fourth series； in which was the juice of the interior of the grapes； remained equally free from change； although I was not always able； on account of the delicacy of the experiment； to eliminate every chance of error。 These experiments cannot leave the least doubt in the mind as to the following facts：
Grape…must； after heating； never ferments on contact with the air； when the air has been deprived of the germs which it ordinarily holds in a state of suspension。
〃The boiled grape…must ferments when there is introduced into it a very small quantity of water in which the surface of the grapes or their stalks have been washed。
〃The grape…must does not ferment when this washing…water has been boiled and afterwards cooled。
〃The grape…must does not ferment when there is added to it a small quantity of the juice of the inside of the grape。
〃The yeast； therefore； which causes the fermentation of the grapes in the vintage…tub comes from the outside and not from the inside of the grapes。 Thus is destroyed the hypothesis of MM。 Trecol and Fremy； who surmised that the albuminous matter transformed itself into yeast on account of the vital germs which were natural to it。 With greater reason； therefore； there is no longer any question of the theory of Liebig of the transformation of albuminoid matter into ferments on account of the oxidation。〃
FOREIGN ORGANISMS AND THE WORT OF BEER
〃The method which I have just followed；〃 Pasteur continues； 〃in order to show that there exists a correlation between the diseases of beer and certain microscopic organisms leaves no room for doubt； it seems to me； in regard to the principles I am expounding。
〃Every time that the microscope reveals in the leaven； and especially in the active yeast； the production of organisms foreign to the alcoholic yeast properly so called； the flavor of the beer leaves something to be desired； much or little； according to the abundance and the character of these little germs。 Moreover； when a finished beer of good quality loses after a time its agreeable flavor and becomes sour； it can be easily shown that the alcoholic yeast deposited in the bottles or the casks； although originally pure； at least in appearance； is found to be contaminated gradually with these filiform or other ferments。 All this can be deduced from the facts already given； but some critics may perhaps declare that these foreign ferments are the consequences of the diseased condition； itself produced by unknown causes。
〃Although this gratuitous hypothesis may be difficult to uphold； I will endeavor to corroborate the preceding observations by a clearer method of investigation。 This consists in showing that the beer never has any unpleasant taste in all cases when the alcoholic ferment properly so called is not mixed with foreign ferments； that it is the same in the case of wort； and that wort； liable to changes as it is； can be preserved unaltered if it is kept from those microscopic parasites which find in it a suitable nourishment and a field for growth。
〃The employment of this second method has； moreover； the advantage of proving with certainty the proposition that I advanced at firstnamely； that the germs of these organisms are derived from the dust of the atmosphere； carried about and deposited upon all objects； or scattered over the utensils and the materials used in a brewery…materials naturally charged with microscopic germs； and which the various operations in the store…rooms and the malt…house may multiply indefinitely。
〃Let us take a glass flask with a long neck of from two hundred and fifty to three hundred cubic centimetres capacity； and place in it some wort； with or without hops； and then in the flame of a lamp draw out the neck of the flask to a fine point； afterwards heating the liquid until the steam comes out of the end of the neck。 It can then be allowed to cool without any other precautions； but for additional safety there can be introduced into the little point a small wad of asbestos at the moment that the flame is withdrawn from beneath the flask。 Before thus placing the asbestos it also can be passed through the flame； as well as after it has been put into the end of the tube。 The air which then first re…enters the flask will thus come into contact with the heated glass and the heated liquid； so as to destroy the vitality of any dust germs that may exist in the air。 The air itself will re…enter very gradually； and slowly enough to enable any dust to be taken up by the drop of water which the air forces up the curvature of the tube。 Ultimately the tube will be dry； but the re…entering of the air will be so slow that the particles of dust will fall upon the sides of the tube。 The experiments show that with this kind of vessel； allowing free communication with the air； and the dust not being allowed to enter； the dust will not enter at all events for a period of ten or twelve years； which has been the longest period devoted to these trials； and the liquid； if it were naturally limpid； will not be in the least polluted neither on its surface nor in its mass； although the outside of the flask may become thickly coated with dust。 This is a most irrefutable proof of the impossibility of dust getting inside the flask。
〃The wort thus prepared remains uncontaminated indefinitely； in spite of its susceptibil
