We can now understand the nature of modern neo-vitalism. It borrows from its predecessor its fundamental principle—namely, the specificity of the _vital fact_. But this specificity is no longer _essential_, it is only _formal_. The difference between it and the physical fact grows less and almost vanishes. It consists of a diversity of mechanisms or executive agents. For example, digestion transforms the alimentary starch in the intestines into sugar; the chemist does the same in his laboratory, only he employs acids, while the organism employs special agents, ferments, in this case a diastase. It is a particular form of chemistry, but still it is a chemistry. That is how Claude Bernard looked at it. The vital fact was not fundamentally distinguished from the physico-chemical fact, but only in form. This expurgated and accommodated vitalism (Claude Bernard pushed his concessions so far as to call his doctrine “physico-chemical vitalism”) was revived a few years ago by Chr. Bohr and Heidenhain. Other biologists, instead of attributing the difference between the phenomena of the two orders to the manner of their occurrence, seem to admit the complete identity of the mechanisms. It is no longer then in itself, individually, that the vital act is particularized, but in the manner in which it is linked to others. The vital order is a series of physico-chemical acts realizing an ideal plan. Neo-vitalism has therefore assumed two forms, one the more scientific and the other the more philosophical. _Chr. Bohr and Heidenhain._—Its scientific form was given to it by Chr. Bohr, an able physiologist at Copenhagen, and by Heidenhain, a professor at Breslau, who was one of the lights of contemporary German physiology. The course of their researches led these two experimentalists, working independently, to submit to fresh investigation the ideas of Lavoisier and those of Bichat, on the relation of physico-chemical forces to the vital forces.