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 of Haeckel, the idioblasts of Hertwig, the pangenes of de Vries, the plasomes of Wiesner, the gemmules of Darwin, and the biophores of Weismann.

Biologists who have not got all that they hoped from microscopic structure are therefore thrown back on hyper-microscopic structure.

It is very remarkable that all this profound knowledge of structure has been so sterile from the point of view of the knowledge of cellular functional activity. All that is known of the life of the cell has been revealed by experiment. Nothing has resulted from microscopic observation but ideas as to configuration. When it is a question of giving or imagining an explanation of vital facts, of heredity, etc., biologists unable to supply anything beyond the details of structure revealed by anatomy have had recourse to hypothetical elements, gemmules, pangenes, biophores, and different kinds of determinants.

Anatomy never has explained and never will explain anything. "Happy physicists!" wrote Loeb, "in never having known the method of research by sections and stainings! What would have happened if by chance a steam engine had fallen into the hands of a histological physicist? How many thousands of sections differently stained and unstained, how many drawings, how many figures, would have been produced before they knew for certain that the machine is an engine, and that it is used for transforming heat into motion!"

The study of physical properties, continued on rational hypotheses, has also thrown some light on the possible constitution of living matter. The gap between microscopical structure and molecular or chemical structure has thus been filled.