Page:Thruston speech upon the progress of medicine 1869.djvu/19

17 pointed out the relation of his researches to physiology—their important bearing upon the subjects of absorption, digestion, the coagulation of the blood—upon cadaveric rigidity, and I may add, upon the many processes of fermentation and putrefaction. In his method of dialysis also, we have at once an instrument of great power, and a means of classifying the phenomena which it brings to light.

All these researches are important aids to the study of physiology, and throw light upon the physical conditions of life. There are, in fact (as I have ventured before to point out), four chief conditions of molecular action, all of which are constantly fulfilled by living organized structures.
 * 1) The possession of a power of molecular attraction.
 * 2) A loose aggregation of molecules.
 * 3) Low chemical affinity.
 * 4) Perfect purity of molecules.

These conditions are present in nearly all physiological processes; by living beings, freshly formed, or nascent, material is continually brought forth with its molecules free, untainted by any soil of extraneous matter, and it is at once presented to fluids containing substances for which it has more or less molecular affinity.

For the most part, again, this material is colloidal in its structure, and hence is both chemically indifferent, and with its particles loosely aggregated, and in a position to act powerfully without entering into chemical combination; and, as Dr Graham has shown, it is readily penetrated by gases and crystalloidal substances.

The so-called ferments are the most prominent and decided possessors of these properties, and probably owe their peculiar powers to this fact; and we can scarcely