1838, Turpin compared the Torulæ to the ultimate elements of the tissues of animals and plants. The elementary organs of their tissues, which might be compared to the minute vegetable growths found iii common yeast, are likewise decomposers of those substances which environ them.
Almost at the same time, and, probably, equally guided by his study of yeast, Schwann was engaged in those remarkable investigations into the form and development of the ultimate structural elements of the tissues of animals, which led him to recognize their fundamental identity with the ultimate structural elements of vegetable organisms.
The yeast-plant is a mere sac, or "cell," containing a semifluid matter, and Schwann's microscopic analysis resolved all living organisms, in the long-run, into an aggregation of such sacs or cells, variously modified; and tended to show that all, whatever their ultimate complication, begin their existence in the condition of such simple cells.
In his famous "Mikroskopische Untersuchungen" Schwann speaks of Torula as a "cell," and, in a remarkable note to the passage in which he refers to the yeast-plant, Schwann says:
I have been unable to avoid mentioning fermentation, because it is the most fully and exactly known operation of cells, and represents, in the simplest fashion, the process which is repeated by every cell of the living body.
In other words, Schwann conceives that every cell of the living body exerts an influence on the matter which surrounds and permeates it, analogous to that which a Torula exerts on the saccharine solution by which it is bathed—a wonderfully suggestive thought, opening up views of the nature of the chemical processes of the living body, which have hardly yet received all the development of which they are capable.
Kant defined the special peculiarity of the living body to be that the parts exist for the sake of the whole, and the whole for the sake of the parts. But when Turpin and Schwann resolved the living body into an aggregation of quasi-independent cells, each like a Torula, leading its own life and having its own laws of growth and development, the aggregation being dominated and kept working toward a definite end only by certain harmony among these units, or by the superaddition of a controlling apparatus, such as a nervous system, this conception ceased to be tenable. 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 Torulæ which float in beer-wort.
Schwann burdened his enunciation of the "cell-theory" with two false suppositions: the one, that the structures he called "nucleus"
