are also a great mass of indistinct diseases, presenting themselves under no form clearly characterized, nor exactly recognized as having occurred before, and to which of course the application of no particular substance can be known to have been made, nor its effect on the case experienced. These may be called unknown cases, and they may in time be lessened by the progress of observation and experiment. Observing that there are in the construction of the animal system some means provided unknown to us, which have a tendency to restore order, when disturbed by accident, called by physicians the _vis medicatrix naturæ_, I think it safer to trust to this power in the unknown cases, than to uncertain conjectures built on the ever-changing hypothetical systems of medicine. Now, in the Veterinary department all are unknown cases. Man can tell his physician the seat of his pain, its nature, history, and sometimes its cause, and can follow his directions for the curative process--but the poor dumb horse cannot signify where his pain is, what it is, or when or whence it came, and resists all process for its cure. If in the case of man, then, the benefit of medical interference in such cases admits of question, what must it be in that of the horse? And to what narrow limits is the real importance of the Veterinary art reduced? When a boy, I knew a Doctor Seymour, neighbor to our famous botanist Clayton, who imagined he could cure the diseases of his tobacco plants; he bled some, administered lotions to others, sprinkled powders on a third class, and so on--they only withered and perished the faster. I am sensible of the presumption of hazarding an opinion to you on a subject whereon you are so much better qualified for decision, both by reading and experience. But our opinions are not voluntary. Every man's own reason must be his oracle. And I only express mine to explain why I did not comply with Mr. Carver's request; and to give you a further proof that there are no bounds to my confidence in your indulgence in matters of opinion.