Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/17

Rh opinion still maintained its ground, even when the structure of the tissues became more accurately known. Nor did the plant-like growth of the component parts of the ovum abolish the assumed essential difference of the growth of the vascular tissues.

A very important advance was made in the year 1837, when an actual growth of the elementary particles of epithelium was proved to take place without vessels. Henle (Symbole ad anatomiam vill. intest. Berol. 1837) showed that the cells in the superficial layers of epithelium are much more expanded than those in the deeper strata, a fact which leaves scarcely any doubt as to their true plant-like (i. e. non-vascular) growth. Henle says (l. c. p. 9), “Hoe in loco (in planta pedis) cellularum (retis Malpighii) diametrum extrorsum augeri, saepius repetita observatione pro re certa affirmare audeo. Quas retis cellulas non minus in foetu suillo sensim increscentes transire in cellulas epidermidis, nunquam noninveni.” Purkinje and Raschkow (Meletem. circa mammal. dentium evol. Vratisl. 1835) had made the following observations upon the development of the epidermis: “In primis evolutionis periodis—squamule—epithelii nondum ita conformatae sunt ut in illa periodo, que partui praecedit, sed parenchyma plantarum cellulis simillimum ostendunt, cum quaeque squamula, quae postea talis apparet, tune temporis tanquam cellula polyedrica e membrana tenacissima constans globosamque guttulam continens in conspectum veniat. Pressu applicato rumpebantur istae cellulae atque lymphaticum liquorem effundebant, que cellulae, procedente evolutione, verisimile complanatz in illas polyedricas squamas mutantur.” Henle, when quoting this passage, adds (l. c. p. 9): “Haec illa num vero sola compressio in causa esse possit, ut parva cellula