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Updated: June 3, 2025
Though, as formulated by Schwann and Schleiden, the cell-doctrine has undergone qualifications of statement; yet the qualifications have not been such as to militate against the general proposition that organisms visible to the naked eye, are severally compounded of invisible organisms using that word in its most comprehensive sense.
Indeed, the cell-like character of certain animal tissues had come to be matter of common note among students of minute anatomy. Schwann felt that this similarity could not be mere coincidence, but he had gained no clew to further insight until Schleiden called his attention to the nucleus.
A closer study of animal tissues under the microscope showed, particularly in the case of embryonic tissues, that "opaque spots" such as Schleiden described are really to be found there in abundance forming, indeed, a most characteristic phase of the structure.
Notwithstanding the high authority of Schleiden, therefore, it seems impossible to reconcile his estimates with facts commonly observed and well established by competent investigators. Balance of Conflicting Influences of Forest on Atmospheric Heat and Humidity.
And by cell Schwann meant, as did Schleiden also, what the word ordinarily implies a cavity walled in on all sides. He conceived that the ultimate constituents of all tissues were really such minute cavities, the most important part of which was the cell wall, with its associated nucleus.
The air at the poles revolves upon itself without moving forward; at the equator, the velocity, as we have mentioned, is enormous. If, then, says Professor Schleiden, we imagine the air from the pole to be carried to the equator, some time must elapse before it will acquire the same velocity of motion from west to east which is always found there.
This was supplemented a little later by Fleming's Omnis nucleus e nucleo, when still more refined methods of observation had shown that the part of the cell which always first undergoes change preparatory to new cell-formation is the all-essential nucleus. Thus the nucleus was restored to the important position which Schwann and Schleiden had given it, but with greatly altered significance.
I was ignorant at the time of the thousands of acute intellects engaged in the same pursuit as myself, and with the advantages of instruments a thousand times more powerful than mine. The names of Leeuwenhoek, Williamson, Spencer, Ehrenberg, Schultz, Dujardin, Schact, and Schleiden were then entirely unknown to me, or if known, I was ignorant of their patient and wonderful researches.
As examples and a proof of the strong humanitarian influence Jewish history exercises upon Christians, I would point to the relation established between the Jews and two celebrities of the nineteenth century, Schleiden and George Eliot.
Schwann had regarded cell growth as a kind of crystallization, beginning with the deposit of a nucleus about a granule in the intercellular substance the cytoblastema, as Schleiden called it. But Von Mohl, as early as 1835, had called attention to the formation of new vegetable cells through the division of a pre-existing cell.
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