As I have spoken of climate in the broad sense as accountable for some peculiarities of the health of our women, so also would I admit it as one of the chief reasons why work among men results so frequently in tear as well as wear.  I believe that something in our country makes intellectual work of all kinds harder to do than it is in Europe; and since we do it with a terrible energy, the result shows in wear very soon, and almost always in the way of tear also.  Perhaps few persons who look for evidence of this fact at our national career alone will be willing to admit my proposition, but among the higher intellectual workers, such as astronomers, physicists, and naturalists, I have frequently heard this belief expressed, and by none so positively as those who have lived on both continents.  Since this paper was first written I have been at some pains to learn directly from Europeans who have come to reside in America how this question has been answered by their experience.  For obvious reasons, I do not name my witnesses, who are numerous; but, although they vary somewhat in the proportion of the effects which they ascribe to climate and to such domestic peculiarities as the overheating of our houses, they are at one as regards the simple fact that, for some reason, mental work is more exhausting here than in Europe; while, as a rule, such Americans as have worked abroad are well aware that in France and in England intellectual labor is less trying than it is with us.  A great physiologist, well known among us, long ago expressed to me the same opinion; and one of the greatest of living naturalists, who is honored alike on both continents, is positive that brain-work is harder and more hurtful here than abroad, an opinion which is shared by Oliver Wendell Holmes and other competent observers.  Certain it is that our thinkers of the classes named are apt to break down with what the doctor knows as cerebral exhaustion,—­a condition in which the mental organs become more or less completely incapacitated for labor,—­and that this state of things is very much less common among the savans of Europe.  A share in the production of this evil may perhaps be due to certain general habits of life which fall with equal weight of mischief upon many classes of busy men, as I shall presently point out.  Still, these will not altogether account for the fact, nor is it to my mind explained by any of the more obvious faults in our climate, nor yet by our habits of life, such as furnace-warmed houses, hasty meals, bad cooking, or neglect of exercise.  Let a man live as he may, I believe he will still discover that mental labor is with us more exhausting than we could wish it to be.  Why this is I cannot say, but it is not more mysterious than the fact that agents which, as sedatives or excitants, affect the great nerve-centres, do this very differently in different climates.  There is some evidence to show that this is also the case with narcotics; and perhaps a partial explanation may be found in the manner in which the excretions are controlled by external temperatures, as well as by the fact which Dr. Brown-Sequard discovered, and which I have frequently corroborated, that many poisons are retarded in their action by placing the animal affected in a warm atmosphere.