Or if, descending again in the series, we make the progress of development the basis of our views, and follow this downwards from more general forms to those which are successively subordinate, even as far as to families and individuals of the same species, we connect the subject of hereditary aberrations with this more general law; finding reason from analogy to expect that such should occur, and that they should be carried into extreme variety and minuteness. The different parts of structure and function become more special, or individual, at each step of descent; never losing, however, their relation to the original common type; and in the instances at least of individuals of the same species, tending ever to recur to it, when the causes of change are modified or withdrawn.

This manner of pursuing the inquiry, through the unity or analogy of structure in corresponding organs, is probably the most conformable to nature, and the most likely to lead to correct conclusions from the facts observed. Among other results already obtained from it, is a more just view as to the nature of what have been termed monsters; which, though still regarded as deviations, more or less, from the natural type, are so for the most part in the sense of an interference or arrest at particular periods of development; displacing organs only partially evolved, or suspending the progress of structure in parts yet imperfect. The advance here, from the old notion of a lusus naturæ, is obvious; and the

and designed ; — the points are fixed at which each deviation has its beginning from the more common antecedent forms; -the limit of change is fixed in each particular case. If there be an argument for the unity of creation, more complete and comprehensive than another, it is that which is furnished by the recent progress of comparative anatomy; enabling the observer, by the uniformity of general laws, to predicate from a single minute part of structure all the more important generic characters of the animal to which it belongs.

details into which the doctrine has been carried form a remarkable feature in physiological science. Though exceptions exist to the law propounded by some naturalists, that every particular monstrosity in man has its analogy in the natural state of the same parts in some inferior animal, the fact is nevertheless so general as to justify its being regarded as a principle in the development of animal life.*

It can scarcely be needful to say, that these views are simply illustrative of relation in a series of effects. While augmenting our knowledge in this way, and leading us up to the threshold of the mystery, they give us no power to pass beyond it. The insuperable nature of the limit is even rendered more obvious, when thus approached, than as it is seen from more distant points of view. While we find cause for wonder at the transmission of resemblances from parent to offspring, we must admit the wonder to be equal that there should ever be deviation from this likeness. The one case is in reality as great a miracle to our understanding as the other.

The hereditary tendency to disease, regarding the subject in its most general light, shows itself either in the anormal conformation of particular organs or textures;-or in the presence and transmission from parent to offspring of certain morbid products, either altogether new, or vitiated in kind, or faulty by excess. Pursuing the subject more closely, it may be inquired,

The "Histoire des Anomalies de l'Organization et des Monstruosités," by M. Isidore St. Hilaire (1832-36), contains all that is known on this subject;-expounded according to Serres's doctrine of centripetal development, in opposition to that which has been termed centrifugal, from opposite views as to the progressive formation of organs.

I have not used the term monstrosity here, as this in common language expresses only extreme cases of mal-conformation; depending, it may be, on the same principles, but from obvious causes more generally prevented from becoming hereditary.

whether these morbid products are in reality all referrible, as effects, to variations in some part of organic structure, producing or evolving them; so that the solids of the body alone, by their conformation and texture, carry on such peculiarities through successive generations? or, whether the animal fluids also, and particularly the blood, may not be concerned in the transmission thus taking place?

This is a question involving much curious but doubtful speculation, nor does the actual state of our knowledge afford any certain answer to it. We can go little further than to say, that the evidence as to the solid structure of the body, and the changes they severally undergo, is more distinct and complete; but we are not justified in denying that the blood may also take on morbid conditions, directly transmissible to offspring. The question here, in truth, involves the origin of the blood itself, in relation to these solid parts; and merging in this, its import to the subject before us is less than might at first be supposed. So close is the mutual connexion between them and the blood, in growth, function, and change, that it is scarcely possible, even were it practically needful, to separate the two in this inquiry. The faulty organization of certain parts of the former may produce morbid changes in the latter or the fluids of the body, already vitiated from other cause, may alter and deprave the texture of the solid parts.

If there were reason for going further into this question, it might fairly be argued, that, however difficult to conceive a fluid like the blood, ever in motion and change, being capable of hereditary taint, yet is not this really more difficult to understand than a character or peculiarity conveyed by descent to any part of the solids of the body. The blood has vitality in every sense in which we can assign it to the latter. Under some views it is the portion of the animal frame which

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is especially so endowed. Its first appearance in the area vasculosa of the germinal membrane of the embryo, is prior to the existence of those very organs which, after birth, chiefly minister fresh materials to it: and though undergoing constant change, it has this in common with the animal solids; and with those equally, which are most frequently the subjects of hereditary affection. The morbid changes, moreover, which it undergoes, are often the effect of inconceivably minute portions of foreign matter brought into the circulation; as denoted in the effect of various poisons, in the exanthematous disorders, and other instances familiar in the history of disease.

This part of the subject, then, can be approached only through general views, and subject to the obscurity which covers the whole. Yet even these general views, as far as they are reasonably supported by analogy or otherwise, have their value to medical science. We are called upon to recognize certain constitutional diseases, continued from one generation to another, the material of which (if such phrase is permissible for what cannot be presented in separate form) can only be conceived as circulating in the blood, and conveyed thereby to the parts or organs which it affects with the characters of visible disease. These constitutional disorders, and their results, will be found to comprise under a few really specific differences, very many forms of disease, scattered through our nosologies under different names and distinctions. Their relations to certain common morbid principles (an inquiry of great importance in every way) are often expounded or confirmed by looking to the fact of hereditary transmission; and to the agency of the blood, as containing in itself the elements of disease, or as conveying them to different parts of the body.

Regarding, then, this great principle of the transmission

of bodily peculiarities from the parent to the offspring, it will be seen that we cannot yet rightly distinguish what belongs to the blood-what to the solid textures of the body what to the connexions and mutual agency of both. Nevertheless, we may find here a convenient basis for the general arrangement of facts, where the latter are so numerous and varied as to need some method for their fit observation. Our imperfect knowledge leaves much that cannot be submitted even to the broadest lines of distinction; but in this, as in other sciences yet unformed, facts, truly determined, will best lead to correct classification and future laws.

Looking first to examples of the anormal conformation of particular organs, transmitted by descent, and limiting the consideration to man, we find the variety almost beyond estimate. Here, indeed, a view occurs in the outset, of great interest to the inquiry, but which I do not think to have been hitherto sufficiently regarded.

If peculiarities of external form and feature, whencesoever originally derived, tend so speedily to become hereditary,— affecting, as we see on every side, not families alone, but, by intermixture and descent, whole races of mankind,-we can have no doubt that deviations of internal structure (whether they be of deficiency or excess, or of any other nature) are similarly transmitted; and with them propensities to, or conditions of, morbid action in the parts thus organized. Though the direct proof is not equal for the two cases, and though the effects resulting are of such different importance, yet is it certain that the peculiarities, so carried on from one generation to another, have reference for both to one common law. Those deviations from the primitive or common type of the species, which occur chiefly in the bony structure, integuments, or muscular fabric, producing varieties in the outward form and feature, in the texture or colour of the skin,