ERRATA.

Page 60, in the note, for pathologici, read pathologicæ. 63, ninth line from the bottom, for are, read as. 93, ninth line from the top, for springs, read spring. 165 and 166, for haemoptysis, read hæmoptysis. 175, for Hale Townsend, read Hare Townsend.

INTRODUCTION.

THE fact that the material elements of all organic beings-plants and animals-originate from minute cell-organisms, was first announced by OKEN; * it has been ably illustrated and enforced by Schleiden, Schwann, Barry, and other physiologists; and is now universally concurred in, as a truth of the highest interest and importance to physiology, and practical medicine. The organisms here spoken of, and variously termed, vesicles, corpuscles, or cells, are microscopic objects, usually of a globular or oval figure, various in colour, and consist of four parts, an exterior integument, a nucleus, and an interior viscous or granular matter, mixed with molecules.

The exterior integument, or cell membrane, is a thin homogeneous pellicle, through which the interior contents of the cell may be discerned: the nucleus is an

* Die Zeugung. Frankfurt, 1805.

B

apparently compact body, adherent to some point of the cell membrane; and the viscous or granular matter and molecules are the ingredients to which the sensible properties or qualities of the cell, and the characteristics of the materials formed by its morphology must be referred. In their original process of production, these cell-organisms have been regarded by Oken as the primary forms whence all larger and more compound structures were originally evolved. Without entering upon the merits of this general theory, it is quite true that microscopic cells abound in every department of life, and that they are the only material elements of the early human embryo.

Recent improvements in the microscope having placed these elementary organisms within the sphere of visual analysis, and demonstrated their universality in the structure and secretions of animal bodies and man; have thereby altered the value of anatomical researches, conducted without a suspicion of their existence; and conclusions based upon views with the unaided eye alone, to which these organisms are quite invisible, must be amended or abandoned. So the multiform changes wrought in the textures of the human body by scrofula and inflammation have been topics of anxious and unwearied investigation from the period anatomical studies commenced; but if a microscopical analysis of the healthy tissues shows the physiological conclusions derived from an unaided visual anatomy to require revision and amendment, then it follows necessarily that patho

logical conclusions derived from the same source must undergo a similar revision.

It is not long since earth, air, and water were considered and treated of in chemical works as elements; but when it was proved that they are compound bodies, it became necessary to review the phenomena in which they take part, and to assign to each component its appropriate place and proper agency in every change effected. So when blood was deemed a homogeneous fluid, and capillary vessels to be simply tubes, they were looked upon as agents; but now, when we know from microscopical demonstration that blood consists of various cell-organisms floating in a fibrillating fluid, and that capillary vessels are not simple tubes, it becomes necessary to determine the part which each element performs in the phenomena of growth, nutrition, and disease. The fact being that the microscope has placed physiology and pathology in a position analogous to that of chemistry at the æra of the discoveries of Watt, Cavendish, and Priestly.

In passing, by means of the microscope, from the confines of the visible to those of the invisible domain of matter, we must bear in mind that the latter or the invisible is quite as important as the former or the visible; for all objects become invisible long before we arrive at the end of their composition.

The ultimate atoms or forms of oxygen, nitrogen, carbonic acid, and water, surrounding us, and as we inhale or exhale them, cannot be rendered visible by the