changes take place in the adventitious structures, both as regards the successive development of parts and the changes effected in such a structure, or even in parts of it when produced.

I have elsewhere had occasion to notice that from a tumour having all the closeness and firmness of schirrus, a new growth may proceed, having the softness and rapid increase of fungoid disease. The most distinct specimens of compound adventitious serous cysts which form the type of this group of structures, which in their appearance so closely resemble the normal tissues that they cannot be regarded as malignant, and which from their want of influence on surrounding parts, and on the system generally, justify their benign character, will sometimes give origin to a fresh growth on some part of the tumour which they constitute, presenting all the characters of a truly malignant adventitious structure. often find melanosis combined with another variety of the same class, and when, as is sometimes the case, a succession of operations are performed at the same part for the extirpation of the tumour, there is a progressive alteration in the physical as well as chemical characters of the adventitious structure, which is constant only in exhibiting the type of compound serous cysts upon which I have so long insisted.

We

It will, I hope, be generally understood that these remarks are not designed to underrate or discourage any extent of chemical investigation which may be devoted to the subject, but merely to point

out the objections to which it is liable when in its present state it is appealed to as a distinctive test, except as between varieties.

Dr. Carswell has urged an objection against development through the production of compound serous cysts, as pointed out by myself, which is adopted by his successor, as well as by Professor Grose, of Cincinnati, who regards it as triumphant. An objection sanctioned by such authorities is too important to be allowed to pass without consideration, either to be received as a correction, or to be refuted if invalid. The Professor observes that there is an ambiguity as to whether the cysts produce their contents or are produced by them, and that in the latter case their importance is overrated, and that the adoption of the reflected serous membrane as a type, attributes to the adventitious structure a position which in fact is exterior to the investing membrane, precisely as the heart is not literally inclosed in the pericardium.

I shall notice the latter objection first, as being of the more tangible character, and preparing the way to the better understanding of the former.

For the comprehension of this, as well as of almost every question connected with the subject in which anatomical character is concerned, I would appeal to the ovarian cysts, which are not only examples on a large scale, but much less liable to obscurity through alterations produced by successive change.

Let us commence with a large containing sac.

This has, like other parts within the abdomen, an extensive covering of peritoneum : in fact, it has its close and reflected portions, and this very membrane may serve as an illustration of the Doctor's objection, seeing that this membrane is wanting as a covering at the more or less extensive base of attachment of the tumour.

The peritoneum is the accessary, and not the essential part of the tumour. This we may find, as to bulk, chiefly to consist of the peculiar fluids which may be withdrawn by the trochar, and which we find everywhere enclosed by the lining membrane, which forms a perfectly continuous closed sac. The fluid in the sac is therefore partly enclosed by the peritoneum, as the blood in the heart is by the pericardium, but it is perfectly enclosed by the sac, as the blood is by the lining membrane of the heart prolonged into the large arteries and veins and their ramifications.

Let us now consider the second order of cysts that arise in the parietes of the principal one. Each of these commences as a perfectly closed spheroidal sac beneath the lining membrane of the principal one. In the progress of its development it pushes forward the lining membrane of the original sac, beneath which it is formed, and consequently has from this source a close and reflected covering, though these may be widely separated from each other by the copious contents of the first sac, but the broad base or attachment may be so extensive that the very character

of a reflected membrane may, with difficulty, be recognised, or it may be so slender, and the secondary growth so filamentous, that the existence of the second sac may be rather inferred than demonstrated. Sometimes, as I have also shown, in the second sac, in the progress of its development, an opening may be produced through its own membrane and that which invests it, producing a communication between the first and the second, which latter pours its secretion into the larger cavity, and thus becomes a true follicle, probably illustrative of the cellular origin of other follicles. It is needless that I should describe the succession of sacs which not in theory only, but in fact continue to be developed in this mode. Enough I think has been stated to show that on the principle of the formation of reflected membranes, the peculiar matter of the tumour, whether fluid or solid, is not left partially uncovered by membrane. In considering the reflected character, we must not lose sight of the lining membrane, and in considering the tendency to more or less rapid development, we must not lose sight of the subordinate cysts, the development of which produces the reflected form in the membrane, in the parietes of which it has been produced, which reflected character forms an important part in producing the anatomical characters of the mass.

With respect to the other part of the objection, viz., that it is not shown whether the sacs or their contents are first produced, and that it is con

sequently uncertain which is cause and which effect, I may, perhaps, be allowed to observe that I may be content to leave this point in the same situation with others to which it is most intimately allied, I mean all those productions to which a cellular origin is conceded.

Of this description are the pulps of the teeth, which in many respects bear a close analogy to the compound serous cysts observed in the production of the adventitious structures. Whilst yet of microscopic size, we find both cysts and their contents; and in their advance to their ultimate condition, both pursue their changes in mutual dependence on each other.

The membrane, however, in both cases seems to be the more important, seeing that it is, in both, the medium of nutrition, and also in some degree the determiner of form.

I have elsewhere stated that in the neighbourhood of a malignant or cancerous growth, the tendency to contamination of the surrounding structures appeared to be determined by the occurrence of inflammation in these textures-an idea that has been opposed as an hypothesis devoid of proof. The remark originated in the observation of facts, and for its explanation I have merely conjecture to offer. The fact however is of such uniform occurrence, that I have no hesitation in appealing to my most experienced professional brethren for its confirmation, and I think they will unite with me in regard