tially to the amount of embryonic tissue originally stored up in the part.

Abnormal additional centres of embryonic tissue in the embryo result in all kinds of monstrosities, parasitic fetuses, supernumerary fingers and toes, accessory glands, etc. A defective amount of building material in the embryo is responsible for many of the fetal defects, such as hare-lip, cleft palate, absence of or defective limbs, etc. Another familiar instance substantiating the correctness of the theory of the origin of tumors from a matrix of embryonic cells is furnished by the pregnant uterus. As a rule, hypertrophy of tissue is attended and produced by increased physiological function. In the gravid uterus there is an increase of muscular tissue attending simply an increased physiological growth of an organ, unattended by a corresponding increase of function, but preparatory to a sudden emergency requiring great functional activity. During pregnancy the muscular fibres remain in a condition of rest during the intervals between slight muscular contractions first observed and described by Braxton Hicks. The uterus receives an unusual blood-supply. We can explain the attending muscular hyperplasia only by assuming the presence of a superabundant deposit of embryonic cells awaiting a favorable opportunity to develop into mature, functionally-active muscular tissue.

The origin of a tumor from post-natal embryonic tissue is susceptible of a satisfactory explanation. Every surgeon can recall instances. of the development of tumors from inflammatory products-scar-tissue and immature callus. We must take it for granted that in such tissue cells or groups of cells have failed to undergo transformation into mature tissue, and that they perform in the production of tumors the same rôle as the congenital matrix of embryonic cells of Cohnheim. In the absence of a more plausible theory, the writer is forced to conclude that every tumor is the product of tissue-proliferation of a congenital or post-natal matrix of embryonic cells, aroused into activity by a general or local physiological stimulation or by congenital or acquired abnormal conditions in its immediate environment.

II. MORPHOLOGY AND MULTIPLICATION

OF TUMOR-CELLS.

Morphology. The shape of a tumor-cell corresponds very closely to that of the cells of the organ or part in which the tumor originated. In the growth of a tumor the cells retain their original type. The development of the cells of benign tumors ultimately reaches the highest degree of perfection, so that under the microscope it is difficult if not impossible to distinguish between tumor-tissue and the tissue to which it belongs or which it represents. The macroscopical and microscopical resemblance between a lipoma and normal fatty tissue and

FIG. 2.-Embryonal connective tissue:

an adenoma and normal glandular tissue is often almost perfect. The cells of which malignant tumors are composed do not attain maturity; consequently they resemble more closely the fixed tissuecells in their juvenile state. From the illustration showing the shape of young connective-tissue cells (Fig. 2) and sarcoma-cells, it will be seen that their the intercellular substance is only slightly morphology is more nearly identical than would be expected from the difference in their source and the accomplishment of the ultimate object of their existence. The most striking difference between a sarcoma-cell and an immature connective-tissue cell under the microscope is the size and number of the nuclei. The nucleus of the sarcoma-cell is large and often multiple, showing greater vegetative activity as compared with the mononucleated connective-tissue cell. Absence of uniformity of size in the sarcoma-cells is another distinguishing criterion.

differentiated (after Piersol).

Most of the older text-books on pathology contain elaborate descriptions of a morphologically specific cancer-cell. The application of this teaching in practice resulted in many mistakes in diagnosis by placing too much reliance upon the morphological appearances of cells under the microscope. It is stated above that the structure of the cells of benign tumors is so closely akin to that of the normal cells of the part which the tumor represents that the microscope alone cannot be relied upon in distinguishing between the pathological product and the

normal tissue. This assertion will be strengthened by illustrations representing a non-malignant epiblastic tumor and the middle strata of the epidermis.

FIG. 3.-Cells from a spindle-celled sarcoma treated fresh in a solution of sodic chloride; X 250 (after Perls).

In carcinoma, the malignant tumor of the epiblast and hypoblast, the cells again bear a great resemblance to the cells which compose the respective germinal layers. Like sarcoma-cells, they do not attain maturity; consequently they present in their structure more the type

of embryonic than mature epithelial cells. In contradistinction to the normal epithelial cells, we find that many of the carcinoma-cells are polynucleated. The caudate prolongation of many of the cells is not a characteristic feature of a malignant epithelial cell, as was formerly supposed, but is one of the results of rapid cell-growth and pressure

from without. The polymorphism of the cells of malignant tumors is largely due to the combined effect of these two factors in modifying cell-form. The student should remember also that the contour of a cell under the microscope will depend greatly on the direction of the cutting in making the sections. Thus if, in case of a spindle-celled

FIG. 6.-Cells from an epithelial carcinoma of the bladder; X 250 (after Perls).

sarcoma, the section is made in the direction of the long axis of the cell, the cell will present a spindle-shaped appearance; on the other hand, if the cell is cut transversely, it will present an oval outline or will appear round, as in cases of round-celled sarcoma. In conclusion, it must be said that while polymorphism and multiple large nuclei strongly point toward the malignant character of cells, these conditions. cannot be relied upon in making a positive distinction between normal. and benign and malignant tumor-cells.

Karyokinesis. It is now generally conceded that every pathological process has its physiological prototype. Cell-multiplication in disease may arise at a place where it is not needed, or at the wrong time, or to an extent beyond the limits of local normal requirement. Tumor-cells multiply, like most of the normal tissue-cells, by indirect.

division, a process called karyokinesis. This is the method of reproduction of nearly all the fixed tissue-cells of a higher type in the body. This method of cell-segmentation was first described and carefully studied by Flemming, who termed the process karyomitosis. The essential constituents of a cell are the protoplasm and the nucleus. There is a strong tendency at the present time to refer all kinetic changes in the cell-contents to the agency of the nucleus, and to ascribe to the protoplasm the passive rôle of a nutritive substance. In the impregnated ovum influences of nuclear changes have been described, but at the same time it was shown that the protoplasm is capable of automatic as well as responsive action. Pflüger thought that gravitation is the sole guiding factor in segmentation. According to Born, Hertwig, Weismann, and Kölliker, the protoplasm alone is isotropic, but Whitman thinks that this is far from the truth. Others, like Pflüger, believe that the protoplasm contains physiological molecules from which organs are developed. Polarity of the protoplasm and the nucleus. exists independently, and is not reciprocal. Contractions in the unfertilized eggs have been observed. The protoplasm is an active rather than a passive structure. M. Nussbaum was the first to establish the important fact that enucleate pieces of an infusorium are incapable of regenerating lost parts, while nucleate fragments soon regain the specific form. From this observation it will be seen that the nucleus is indispensable to the preservation of the formative energy of the cell, while the protoplasm performs an important but less essential rôle in the reproduction of cells. Nussbaum very correctly asserts that both the protoplasm and the nucleus are necessary in a cell to enable it to perform its specific function and to reproduce its own kind. The nucleus does not change its form except when it is the seat of active kinetic changes, while the form of the cell is changeable and is greatly influenced by its environments.

The researches of Flemming, Strassburger, Bütschli, and others have demonstrated the great importance of the nucleus in the reproduction of cells. The protoplasm under the highest powers of the microscope is seen to consist of a fine reticulum of protoplasmic strings, the meshes of which contain a homogeneous fluid. The mature cell is enveloped by a separate cell-wall. The meshes of a similar network in the nucleus are filled with a granular fluid. According to Carnoy and Mayzel, the nucleus contains, besides, a distinctive substance called "nuclein," or, from its intrinsic capacity to receive and to hold coloring material, "chromatin." The nucleoli in mature cells are globular masses of chromatin, one or several in number. It is the chromatin which, when properly stained, outlines the figures observed during the different