This single illustration covers a wider ground than the special function to which it belongs.  We are learning that the chemistry of the body must be studied, not simply by its ingesta and egesta, but that there is a long intermediate series of changes which must be investigated in their own light, under their own special conditions.  The expression “sum of vital unities” applies to the chemical actions, as well as to other actions localized in special parts; and when the distinguished chemists whom I have just cited entitle their work a treatise on the immediate principles of the body, they only indicate the nature of that profound and subtile analysis which must take the place of all hasty generalizations founded on a comparison of the food with residual products.

I will only call your attention to the fact, that the exceptional phenomenon of the laboratory is the prevailing law of the organism.  Nutrition itself is but one great catalytic process.  As the blood travels its rounds, each part selects its appropriate element and transforms it to its own likeness.  Whether the appropriating agent be cell or nucleus, or a structureless solid like the intercellular substance of cartilage, the fact of its presence determines the separation of its proper constituents from the circulating fluid, so that even when we are wounded bone is replaced by bone, skin by skin, and nerve by nerve.

It is hardly without a smile that we resuscitate the old question of the ‘vis insita’ of the muscular fibre, so famous in the discussions of Haller and his contemporaries.  Speaking generally, I think we may say that Haller’s doctrine is the one now commonly received; namely, that the muscles contract in virtue of their own inherent endowments.  It is true that Kolliker says no perfectly decisive fact has been brought forward to prove that the striated muscles contract without having been acted on by nerves.  Yet Mr. Bowman’s observations on the contraction of isolated fibres appear decisive enough (unless we consider them invalidated by Dr. Lionel Beale’s recent researches), tending to show that each elementary fibre is supplied with nerves; and as to the smooth muscular fibres, we have Virchow’s statement respecting the contractility of those of the umbilical cord, where there is not a trace of any nerves.

In the investigation of the nervous system, anatomy and physiology have gone hand in hand.  It is very singular that so important, and seemingly simple, a fact as the connection of the nerve-tubes, at their origin or in their course, with the nerve-cells, should have so long remained open to doubt, as you may see that it did by referring to the very complete work of Sharpey and Quain (edition of 1849), the histological portion of which is cordially approved by Kolliker himself.