These Lectures and Essays are arranged in the order corresponding to the date of their delivery or publication. They must, of course, be read with a constant reference to these dates, by such as care to read them. I have not attempted to modernize their aspect or character in presenting them, in this somewhat altered connection, to the public. Several of them were contained in a former volume which received its name from the Address called "Currents and Counter-Currents." Some of those contained in the former volume have been replaced by others. The Essay called "Mechanism of Vital Actions" has been transferred to a distinct collection of Miscellaneous essays, forming a separate volume.

I had some intention of including with these papers an Essay on Intermittent Fever in New England, which received one of the Boylston prizes in 1837, and was published in the following year. But as this was upon a subject of local interest, chiefly, and would have taken up a good deal of room, I thought it best to leave it out, trusting that the stray copies to be met with in musty book-shops would sufficiently supply the not very extensive or urgent demand for a paper almost half a century old.

Some of these papers created a little stir when they first fell from the press into the pool of public consciousness. They will slide in very quietly now in this new edition, and find out for themselves whether the waters are those of Lethe, or whether they are to live for a time as not wholly unvalued reminiscences.

March 21, 1883.