_Theodor Schwann, the son of a Prussian printer, was born at Neuss, Prussia, December 7, 1810. He first studied medicine, but was persuaded to devote himself to science by Johannes Mueller, who appointed him assistant in the anatomical museum. In 1838 he was called to the Catholic University of Louvain, and later removed to Liège. One of the first to suggest the chemical explanation of life, he discovered the presence and function of pepsin as a ferment in digestion. In 1839 he established his great theory that all life is composed of inter-connected cellular units--a conception which revolutionized biology. He died at Liège on January 11, 1882._ CELL THEORY[33] The various opinions entertained with respect to the fundamental powers of an organized body may be reduced to two, which are essentially different from one another. The first is, that every organism originates with an inherent power, which models it into conformity with a predominant idea, arranging the molecules in the relation necessary for accomplishing certain purposes held forth by this idea. Here, therefore, that which arranges and combines the molecules is a power acting with a definite purpose. A power of this kind would be essentially different from all the powers of inorganic nature, because action goes on in the latter quite blindly. A certain impression is followed of necessity by a certain change of quality and quantity, without regard to any purpose. In this view, however, the fundamental power of the organism (or the soul, in the sense employed by Stahl) would, inasmuch as it works with a definite individual purpose, be much more nearly allied to the immaterial principle, endued with consciousness which we must admit operates in man.