Diseases of more general site, and which therefore did not fall conveniently under discussion in describing any one part, were reserved for a separate course of lectures. It was in this course that he more fully developed those general principles on which his reputation more especially rests. Of his inimitable manner we shall speak hereafter. He was one of the first who insisted on the great importance of Comparative Anatomy, in studying the uses of the several parts of the human body. Were it not for the comparison of the relations of various parts in different animals, we should be continually the victims of hypotheses, which the juxtaposition or other characters of organs in any _one_ animal are constantly suggesting. Here necessity compels the observance of that rule of inductive philosophy, which seeks not for the true relation of any one thing in _itself_, but from _universals_, from uses and application which are common to _other_ things. In one case nature makes that luminously clear, which is only dimly shadowed forth in another; and in seeing organs under every conceivable variety of circumstance, we learn to estimate at their full value characteristics which are common to and inseparable from all—the only point whence we can securely deduce their real uses in the animal economy. Of this, Abernethy early saw and inculcated the advantages. As it was impossible to combine anything like a comprehensive study of a vast science in the same course with lectures on human Anatomy, he was accustomed, at the conclusion of the course, to devote a lecture or two to select illustrations of this important subject. This he ultimately relinquished, the universal admission of the fact rendering it no longer necessary. We shall have occasion, by and by, to record the circumstances under which one of the most important steps was taken for securing the interests of Comparative Anatomy in this country—a proceeding in a great degree owing to the good sense and personal influence of Abernethy, and exemplifying, in the admirable fitness of the individual[16], the penetrative perception of character which distinguished his early Preceptor in Anatomy. We have little doubt that we have now entered on the most laborious part of Abernethy's life, and that, during this and some succeeding years, his exertions were so great and unremitting, as to have laid the foundation of those ailments which, at a comparatively early period of life, began to embitter its enjoyment, and to strew the onward path with the elements of decay and suffering.