TO THE READER.

THE following papers form the complement of those published some months back under the title of “COMMON MIND TROUBLES.” The whole might have appeared in a single volume with the designation chosen for the present, but it seemed better to issue the two series separately. This I have done, and they follow not inaptly my "MINDS AND MOODS."

I can only repeat what I said in the preface to the last collection of papers: they were not written for professional readers; but for the generous reception accorded to them in quarters where I had no right to expect they would be, even, noticed I must express my obligation. I shall not be sorry if in examining the contents of this little book the reader adopts a practice familiar to the impatient devourer of fiction, and attacks the last chapter first.

When reviewers complain that I do not prescribe for my readers they pay me the best of compliments. The sole purpose I have set myself in these papers is to help the worried and weak to avoid the peril of mind disease. Medical men cannot, however much they may feel disposed to, impart to laymen that knowledge of disease without which it is an act of audacity to undertake the treatment of the simplest affection, and they are not, in my opinion, justified in addressing the unskilled community in works which, while they pretend to counsel, cannot fail to mislead. Meanwhile, I am not less strongly convinced that it is the bounden duty of every professor of physic to do all that lies in his power to promote the health of the people. It is his mission to preach the gospel of health. I am trying to do this, so far as I am able.

J. MORTIMER GRANVILLE.

April, 1879.

TEMPERATURE.

SUCH expressions as a "cool head," "hot-headed," and the like, commonly relate to temperament rather than temperature; but it is essential to a full comprehension of the subject before us that the rationale of animal heat should be stated, and the laws that govern the phenomenon of temperature actual and subjective, at least cursorily, explained.

Heat and the sensation of heat are two widely different states. When, on a chilly day or after washing in cold water, a man rubs his hands until a glow of heat seems to suffuse them, there is a very slight rise of actual temperature caused by the friction; the feeling is principally due to nerve-excitement, produced mechanically by the rubbing. The blood flows more freely into, and through, the parts excited immediately afterwards, as shown by the redness, but the first impression of heat is mainly one of sensation. The feeling and the fact are not even constantly related. A person may feel hot when not only the surrounding temperature but that of his

B