by fleep, he changed this ftimuli for an opiate, and finished his business in 40 hours. He then took a glass of wine, and conversed five hours with his employer. The fucceffion of ftimuli in this cafe was first food, next the ftimulus of mental exertion, then wine, then food varied, then punch, then opium, then wine again, and laftly pleafureable conversation.

Some years after that, fays Dr. BROWN, I walked and wandered in all forts of ground, in roads and out of them, over smooth and plain, and heathy and mountainous tracts, from four o'clock after mid-day to two o'clock the next day, with only an hour's reft, and one hearty meal at betwixt ten and eleven in the forenoon, when I was now within fix miles of my destination. The hills over which I wandered in the courfe of the night are those called Lammer-Muir, fituated betwixt Eaft-Lothian and the Mers: the places I travelled between in this route were Edinburgh and Duns. In this great exertion I was fuftained by different ftimuli, which made me insensible to fatigue, the fucceffion of objects, high animal spirits, and love. At the end of my long journey, finding myself among my friends, and the object of my affection, I had ftrength enough ftill remaining to dance with the latter.

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The fame may be observed with regard to medicines, when we wish to increase the tonic power of any ftimulus we should change it, and thus fubftitute bitters for bark, and then recur again to bark or steel. Thus when wine ceafes fufficiently to ftimulate the conftitution, opium or æther, in appropriate dofes, fupplies the defect; and the contrary. This is alfo obferved in the effects of cathartic medicines, for when one lofes its power, another apparently less efficacious will fucceed.

An EXCEPTION to this Influence of Habit.

When the first impression, however, is very strong, and the effect produced very violent, a force or power inferior to the original one will produce the fame effect.

Thus it has often been remarked, that if a perfon, unaccustomed to the use of purgatives, was to take at a dofe 20 grains of aloes, the smartness of the operation would leave fuch a lasting impreffion, that an equal effect would afterwards be produced by one half, one fourth, or even one tenth, of the fame quantity; whereas, had the original dose been only a grain and a half, it might have been necessary to increase it to ten or fiftcen grains, to produce any the leaft effect.

To explain this curious and perplexing phænomenon, we must remind the reader, that the chain of affociated

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actions when weak, being broken, the conflitution is easily disturbed. Thus when a perfon is beginning to learn the alphabet, or the multiplication table, the ideas first get affociated in the order of the table; but should the young scholar skip over three or four steps, his recovery would be then impracticable. And, again, perfons, by a strong emetic, have had their ftomach rendered fo irritable, that afterwards one twentieth of the first dofe has proved a fufficient emetic. It is thus alfo that a fudden and ftrong terror makes a coward for life; and fits that have been brought on by fright, recur when even a lefs occafional caufe fhould chance to prefent itself.

A black fervant in the country, on going to his pantry in the hall, was suddenly shot at by a robber who lay lurking behind a fcreen. The family being alarmed, found the fervant to all appearance dead. He paffed nearly the whole night in fits, and ever after, whenever it thundered much, or he was surprised by a flash of lightning, he was fure to be thrown into fits.

In fuch cases perhaps the fibre is weakened, and the conflitution or temperament is entirely changed; but of this more will be faid when we come to treat on the Nature of Difeafe.

END OF THE SECOND VOLUME.