In the hephir used in Europe for fermenting milk, another symbiotic association of yeast and a bacterium, it is seen that in this process no less than four distinct organisms are concerned. I have already instanced the fermentation of rice to produce saké, which is first acted upon by an Aspergillus that converts the starch into sugar and an associated yeast, and this is also shown to be a distinct fungus, symbiotically associated in the conversion. “Starting, then, from the fact that the constitution of the medium profoundly affects the physiological action of the fungus, there can be nothing surprising in the discovery that the fungus is more active in a medium which has been favourably altered by an associated organism, whether the latter aids the fungus by directly altering the medium, or by ridding it of products of excretion, or by adding gaseous or other body. It is not difficult to see, then, that natural selection will aid in the perpetuation of the symbiosis, and in cases like that of the ginger-beer plant it is extremely difficult to get the two organisms apart, a difficulty similar to that in the case of the soredia of lichens.” Buchner discovered that by means of extreme pressure a something can be extracted from yeast which at once decomposes sugar into alcohol and carbon-dioxide. This something is regarded as a kind of incomplete protoplasm--a body, as we have already seen, composed of proteid--and in a structural condition somewhere between that of true soluble enzymes like invertin and a complete living protoplasm. This reminds me of an older experiment of mine, the immediate conversion of cane-sugar into grape-sugar. If we take two parts of white sugar and rub it up in a mortar with one part of a perfectly dry solid, the German yeast before spoken of, it is immediately transformed as if by magic into a flowing liquid mass--a syrup. This process of forming “invert sugar” can be watched under the microscope; the liberation of carbonic acid gas in large bubbles is seen to go on simultaneously with the assimilation of the dextrose, and the breaking up of the crystals of sugar; the cell at the same time increasing in size as well as in refractive power; a curious state of activity appears to be going on in the small mass, which is very interesting to watch throughout.