"Tamman has also made a number of experiments with solutions of the chlorides and sulphates of the heavy metals, and solutions of phosphates, silicates, ferrocyanides, and other salts. He found that most of these membranes were permeable to the membranogenous solution. According to Tamman, all {120} precipitated membranes are hydrated substances, and some of them, like the ferrocyanide of copper and the tannate of gelatine are, when first formed, entirely comparable to liquid membranes in all their properties. "Graham had already obtained colourless jellies by the interaction of concentrated solutions of ferrocyanide of potassium and sulphate of copper. Buetschli also has recently described the microscopic appearance of precipitated membranes produced by ferrocyanide of potassium and acetate or chloride of iron. "Like Linke and Gustav Rose, Famintzin has obtained spheroidal precipitates by the reciprocal action of concentrated solutions of chloride of calcium and carbonate of potassium. These grow rapidly and suddenly, with concentric layers showing a spherical or flattened nucleus. He also obtained forms resembling sphero-crystals and starch grains. "Harting, Vogelsang, Hansen, Buetschli, and others have studied the structures which are formed by the reciprocal action of chloride of calcium and the alkaline carbonates. Vogelsang has found small calcareous bodies in the amorphous and globular precipitate formed by chloride of calcium and carbonate of ammonium. He describes spheres attached to one another, vesicles, and muriform structures. The number of these spheroids is increased by the addition of gelatine. Hansen has also studied Harting's method for the formation of sphero-crystals by the action of the alkaline carbonates and phosphates on the salts of calcium in presence of albumen and gelatine. He considers that the latter retard the crystallization and assist the formation of the sphero-crystals. "I shall show later on that gelatine and albumen essentially modify the precipitate and do not merely act as catalytic substances. The researches of Famintzin, repeated and extended by Buetschli, show that sphero-crystals are produced by the reaction of chloride of calcium on carbonate of potassium without the presence of gelatine or albumen. Buetschli studied the spheroids of carbonate of lime by means of polarized light, and found that the layers were alternately positively and negatively polarized." {121} Such is the history of morphogenesis as described in 1902 by the authority most qualified for the task, Professor Quinke of Heidelberg.