introduced boiled grape juice into a series of thirty flasks; of these ten were immediately scaled up; into a second ten he dropped a minute quantity of liquid prepared by washing the surface of some ripe untouched grapes; info the third ten he passed some of the same liquid boiled. In forty-eight hours the first ten were unaltered, the second ten were in full fermentation and filled with flakes of mycelium, the third ten were unaffected. There is reason for believing that all saccharine fruits have on their surface spores which remain quiescent till a concurrence of circumstances brings them into contact with the enclosed juices, then subaqueous growth commences accompanied by the decomposition of the sugar. So long as the subaqueous growth continues propagation of the fungus takes place by budding, but as soon as the sugar is exhausted the fungus comes to the surface end forms spores. Saccharomyces cerevisiæ, or common yeast, is seen under the microscope to consist of a multitude of granular cells, diffused through a turbid liquid called yeast water. The cells are about 1-3,000 of an inch in diameter, and, like all other vegetable cells in their simplest stage, consist of a speck of jelly called protoplasm, enclosed in a non-nitrogenous envelope. Yeast is composed principally of albuminous and amylaceous matter, but it contains a large proportion of phosphates of potash and magnesia. The remarkable feature in its composition is its richness in nitrogen. Funguses contain more nitrogen than any other class of plants. The Chanterelle contains 3.62 per cent., Bolefus edulis 4.25, Lactarius deliciosus 4.60, mushroom, 7.26, and yeast 10, so that it closely approaches animal matter. Those Agarics have been selected for comparison because they have been often set before us at our Fungus Foray dinners. Knowing the chemical composition of yeast, we should expect the medium in which it flourishes to contain the nitrogenous and mineral matters which it requires. It has been proved by experiment that yeast will not exert its peculiar action on sugar unless these matters are present in solution.
We all know that if yeast be added to a liquor at a suitable temperature in which melt or some sacchharine fruit has been digested, certain occurrences will ensue. The liquor will slowly become turbid, effervescence will take place from the escape of free carbonic acid, the sweetness will disappear, alcohol will become evident to the taste and smell, and a large increase will take place in the bulk of the fungus.
There are several varieties of sugar much alike in their chemical composition and properties. The two principal are saccharose and glucose. Yeast acts differently on each, so that it will be well to trace back their relation to, and formation from, starch. Starch, chemically, is nothing more than carbon, combined with the elements that compose water in the proportion of six to five. It appears to be the first product of that decomposition of carbonic acid and assimilation of the carbon, which, under the influence of the sun's rays, is continually going on in growing plants. Starch is the basis from which most other vegetable secretions are formed. It is either used up at once by the plant that secretes it, or it may be laid by for future use; sometimes in the tuber as in the potato, in the seed as in corn, or in pith as sago. Saccharose,
