I trust that it is sufficiently obvious to the reader that great uncertainty must necessarily rest upon our knowledge of a disease so varied as this is, and that all our experience of the effects of remedies upon it must be thoroughly sifted, in order to attain to any measure of accuracy. It is a disregard of this important truth, that has made the testimony of medical men so conflicting in regard to the treatment of this disease. I need not spend time to show how the same uncertainty must embarrass us, to a greater or less degree, in our investigation of all other diseases. The errors resulting from this source may be avoided, in part, by observing accurately the changes which arise from the two tendencies that we have been considering, their modes, periods, signs, and accompanying circumstances. The efficacy of this precaution against error is, as I have already hinted, in proportion to the simplicity and uniformity of disease. In disorders which are complicated, and which vary much in their shape and other circumstances, it is exceedingly difficult to decide, how much agency, in bringing about the curative changes, is justly to be referred to the remedies, and how much to the natural energies of the system. Too much credit is very commonly given to medicine, and too little to nature; and sometimes, when some remedy is praised for its efficacy, and the patient and his friends, and perhaps even the physician, think that it has saved his life, it had no agency in promoting his recovery, and perhaps it retarded it. I pass now to the consideration of the fourth class of the causes of the uncertainty of medicine—mental influences. It never should be forgotten in our observation of disease, that we have not to deal with the body alone, but with the body inhabited by a mind, which is connected with every particle of that body by countless nervous filaments, and therefore acting through them upon it, and affecting to a greater or less degree all its diseased conditions.