Logical deduction and scientific research, according to the beliefs and methods of the age, permitted such doctrines to receive for a time the approval of popular assent. But the spirit of inquiry was abroad in the world, and the advance of embryological science soon gave the demonstration that the doctrine of "included germs" had no foundation in fact, and so it was numbered with the errors of the past.
Cuvier, who had with such ability compared the structure of animal organs, and classified the facts of animal life in their statical or anatomical relationship, was a "vitalist," and thought the vital properties of the body a kind of entity—independent of physical or chemical forces.
Bichat sought, by a study of the tissues which composed the organs, to learn the nature of their functions, or the dynamics of the living body. He found that all the various kinds of tissue of the body, though differing in function, were endowed with two common properties—extensibility and contractility.
While he made phenomena depend on the properties of matter, he nevertheless followed Stahl as a "vitalist," and claimed that vital and physical properties are not only distinct from but antagonistic to each other: "The vital properties preserve the living body by counteracting the physical properties that tend to destroy it." Each class of phenomena is under distinct laws, and the conflict between them is active and constant. As one or the other triumphs, life or death results, and "health and disease are but the vicissitudes of the strife."
Life is, by Bichat, defined as "the group of functions that resist death," and is under the direct supervision of a special principle called at different times "soul," "archæon," "psyche," or "vital force." The philosophic theory which postulated this undetermined factor was known by the generic term of "vitalism," which, under Stahl and Bichat, took accurate definition, and deeply impressed its tenets upon the physical, chemical, and physiological sciences of the age.
Entities of some kind presided over the functions of life and the manifestations of matter. A "vital principle" ruled the organic world, and the phenomena of inorganic nature depended upon the presence of some "principle" which existed independent of the matter through which it displayed itself. Material particles, darting from luminous bodies into the eye, produced the sensation of light. Heat and cold depended upon the presence or absence of a material substance called "caloric." Electricity was a subtile, material agent, existing in a "latent" state in all substances, and manifesting great power when liberated from its repose. And so throughout the domain of chemical, physical, and biological phenomena, material entities existed and were manifested in all forms of inorganic and organic bodies, and yet were independent of them.
This was not an age for synthetic work; indeed, not even accurate analytic work, except in simple things, could be performed. These