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maintains its life in fruit juice where it multiplies, and in the soil where it is protected from drying. Direct experiments have demonstrated this.

From its winter abode in the ground it again reaches the sweet juicy fruit by aid of the wind, and of insects and other small animals. Rain may also be effectual in this respect, viz., in the case of fruit growing near the ground. As soon as multiplication goes on in the fruit juice, insects again play an important part in distribution by carrying the cells from fruit to fruit; according to Wortmann wasps are particularly efficacious in this respect in vineyards. Insects are, however, the distributing agents only during a small part of the year, and then only on the sunny days of that period; all through the year the wind carries the cells about with the dust and finally deposits them in large quantities on the fruit.

With regard to typical saccharomycetes recent investigations of Hansen have shown that they likewise pass the winter in the ground, and that sweet juicy fruits are essential breeding places for them, so that they pass through the same circulation in nature as Sacch. apiculatus. The investigations of Müller-Thurgau and Wortmann confirm this. Pasteur was of the opinion that wine yeasts do not spend the winter underground. Hansen's experiments, however, speak against this, since he found living yeast in the soil under the vines in the wineproducing districts of Germany in spring and summer, i.e., at a time when there are no ripe grapes. Hansen has, besides, seeded saccharomycetes in the soil under natural conditions, and has found them living there more than three years after. After finding that the breeding places of saccharomycetes are on sweet juicy fruit he proceeded from this and followed the cells farther on their way during the different seasons of the year. The sac

charomycetes may of course follow, besides the normal circulation, some other accidental and exceptional one. Only the regular annual repetition of the circulation is of interest in relation to a knowledge of this portion of the economy of nature.

Some writers have expressed the view that the breeding places of the saccharomycetes are in the nectar of flowers until the time of ripe fruit, and that the winter is passed in the intestines and excrements of insects and other animals. Hansen's investigations have shown, however, that if they are found in these places at all, it is quite a matter of accident. The author's experiments on insects have also demonstrated this.

Hansen's researches on the circulation of saccharomycetes in nature, and on the amount of micro-organisms in the air at various seasons of the year, have led to the following results, very important to the brewer: (1) Wind and insects are the most important means of transportation of yeast cells in nature, especially the first; (2) dust clouds in the harvest months are rich in strong yeast cells, produced on sweet juicy fruit; and (3) all through the year the open cooling vessels are the chief means by which wild yeast species make their way into the brewery.

The practical outcome of this was that, in the Old and New Carlsberg Breweries in Copenhagen, the ways in the neighbourhood of the cooling vessels were sprinkled with water, so that the dust might not infect the wort, a procedure which was followed in other places. Later, after the pure culture system was introduced, the open cooling vessels were removed from the above breweries and replaced by closed holders for cooling and aërating the

wort.

The cask deposit and likewise impure pitching yeast may

also give rise to infection; before introducing the pure culture system the latter was probably the worst source of infection. If, by any means, wild yeast, etc., makes its way into practice, it may collect in the water pipes, especially at the connections, and these are, therefore, according to Will's experiments, the most dangerous sources of infection if the wort has been once infected; the cracks and crevices in fermenting vessels are also dangerous in this respect. It is therefore very important to keep these places clean. Will's experiments have also clearly shown that the filter bag is a source of danger. But the wind with the dust it carries remains, all the year round, the chief means by which uninvited intruders make their way into the brewery. Combined with this we have the insects in the summer months on sunny days. Now that impure pitching yeast has become rare, the open cooling vessels therefore form the most important and most dangerous source of infection.

SYSTEMATIC.

1. Genus: Saccharomyces, (Meyen) Reess.

(Synonyms: Mycoderma, Persoon; Cryptococcus, Kützing; Torula, Turpin; Hormiscium, Bail.)

Single cell fungi in which vegetative increase takes place by budding and which develop endospores in their interior under certain conditions. Sometimes they may form a typical mycelium.

The various related species here may, as before stated, be grouped according to their action on the various sugars. The following classification is of this kind, and its basis is to be found in Hansen's paper of 1888

1. Those species which ferment maltose, dextrose and saccharose.

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besides brewery yeast species and in general the culture yeasts hitherto investigated.

2. Those species which ferment dextrose and saccharose but not maltose.

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3. Those species which ferment dextrose, but neither saccharose nor maltose.

Example: Sacch. mali Duclauri, Kayser.

4. Those species which ferment dextrose and maltose, but not saccharose.

Example: Sacch n. sp., isolated from the stomach of a bee by the

author.

5. Those species which ferment neither maltose, dextrose nor saccharose.

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6. Those species which can ferment lactose.

Example: Sacch. fragilis, Jörgensen.

The descriptions and investigations of the species given below are from the authors who have established the species in question, and whose names are added to the systematic name of the species. Where the researches of other investigators are given this is specially mentioned.

Saccharomyces cerevisiæ I., Hansen (Figs. 791, 80, 81, 82, 87, 88 and 89), was isolated from a top yeast in an Edinburgh brewery, and found later also in the yeast of a London brewery. The cells in the yeast sediment are, as a rule, large and round (Fig. 87). In film growths at 6° to 15° C. they are for the most part of the same shape as in the sediment yeast, with only isolated abnormal forms (Fig. 88). The size of the spores varies from 2 to 6 μ; there are usually one to four in each cell, seldom five (Figs. 791 and 89). The germination of the spores is represented in Figs. 80, 81 and 82.

At 37° C. no spores develop.

At 36° to 37° C. the first indications are seen after 29 hours.

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FIG. 89.-Saccharomyces cerevisia I., Hansen. First stages of development of the spores. 1000. (After Hansen.)

The temperature limits for film formation are 33° to 34° C. and 6° to 7° C. The species is a vigorous top beer yeast.

We shall describe some of the numerous forms which are employed in the industry.

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