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Moreover, Bail has observed the development of a Torula larger than T. cerevisioe, from a Mucor, a mould allied to Penicillium. It follows, therefore, that the Toruloe, or organisms of yeast, are veritable plants; and conclusive experiments have proved that the power which causes the rearrangement of the molecules of the sugar is intimately connected with the life and growth of the plant.
But, without presuming to discuss a question which leads us into the very arcana of chemistry, the present state of speculation upon the modus operandi of the yeast plant in producing fermentation is represented, on the one hand, by the Stahlian doctrine, supported by Liebig, according to which the atoms of the sugar are shaken into new combinations either directly by the Toruloe, or indirectly, by some substance formed by them; and, on the other hand, by the Thénardian doctrine, supported by Pasteur, according to which the yeast plant assimilates part of the sugar, and, in so doing, disturbs the rest, and determines its resolution into the products of fermentation.
Out of these materials the Toruloe will manufacture nitrogenous protoplasm, cellulose, and fatty matters, in any quantity, although they are wholly deprived of those rays of the sun, the influence of which is essential to the growth of ordinary plants.
Contemporaneously with these investigations a remarkable discovery was made by Cagniard de la Tour. He found that common yeast is composed of a vast accumulation of minute plants. The fermentation of must, or of wort, in the fabrication of wine and of beer, is always accompanied by the rapid growth and multiplication of these Toruloe.
I have never been able to trace the development of Torula into a true mould; but it is quite easy to prove that species of true mould, such as Penicillium, when sown in an appropriate nidus, such as a solution of tartrate of ammonia and yeast-ash, in water, with or without sugar, give rise to Toruloe, similar in all respects to T. cerevisioe, except that they are, on the average, smaller.
So long ago as 1838, Turpin compared the Toruloe to the ultimate elements of the tissues of animals and plants "Les organes élémentaires de leurs tissus, comparables aux petits végétaux des levures ordinaires, sont aussi les décompositeurs des substances qui les environnent."
But, though the notion that the Torula is a creature which eats sugar and excretes carbonic acid and alcohol, which is not unjustly ridiculed in the most surprising paper that ever made its appearance in a grave scientific journal, may be untenable, the fact that the Toruloe are alive, and that yeast does not excite fermentation unless it contains living Toruloe, stands fast.
The cell lives for its own sake, as well as for the sake of the whole organism; and the cells which float in the blood, live at its expense, and profoundly modify it, are almost as much independent organisms as the Toruloe which float in beer-wort.
Now arises the question, are these microzymes the results of Homogenesis, or of Xenogenesis? are they capable, like the Toruloe of yeast, of arising only by the development of pre-existing germs? or may they be, like the constituents of a nut-gall, the results of a modification and individualisation of the tissues of the body in which they are found, resulting from the operation of certain conditions?
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