inflammation, such as hot applications, act by increasing the blood flow.  So intimate is the association between cell activity, as shown in repair and new formation of cells, and the blood flow, that new blood vessels frequently develop by means of which the capacity for nutrition is still more increased.  The cornea or transparent part of the eye contains no blood vessels, the cells which it contains being nourished by the tissue fluid which comes from the outside and circulates in small communicating spaces.  If the centre of the cornea be injured, the cells of the blood vessels in the tissue around the cornea multiply and form new vessels which grow into the cornea and appear as a pink fringe around the periphery; when repair has taken place the newly formed vessels disappear.

The exudate from the blood vessels in various ways assists in repair.  An injurious substance in the tissue may be so diluted by the fluid that its action is minimized.  A small crystal of salt is irritating to the eye, but a much greater amount of the same substance in dilute solution causes no irritation.  The poisonous substances produced by bacteria are diluted and washed away from the part by the exudate.  Not only is there a greater amount of tissue fluid in the inflamed part, but the circulation of this is also increased, as is shown by comparing the outflow in the lymphatic vessels with the normal.  The fluid exudate which has come from the blood and differs but slightly from the blood fluid exerts not only the purely physical action of removing and diluting injurious substances, but in many cases has a remarkable power, exercised particularly on bacterial poisons, of neutralizing poisons or so changing their character that they cease to be injurious.

We have learned, chiefly from the work of Metschnikoff, that those white corpuscles or leucocytes which migrate from the vessels in the greatest numbers have marked phagocytic properties, that is, they can devour other living things and thus destroy them just as do the amoebae.  In inflammations produced by bacteria there is a very active migration of these cells from the vessels; they accumulate in the tissue and devour the bacteria.  They may be present in such masses as to form a dense wall around the bacteria, thus acting as a physical bar to their further extension.  The other form of amoeboid cell, which Metschnikoff calls the macrophage, has more feeble phagocytic action towards bacteria, and these are rarely found enclosed within them.  It is chiefly by means of their activity that other sorts of substances are removed.  They often contain dead cells or cell fragments, and when haemorrhage takes place in a tissue they enclose and remove the granules of blood pigment which result.  They often join together, forming connected masses, and surround such a foreign body as a hair, or a thread which the surgeon places in a wound to close it.  They may destroy living cells, and do this seemingly when certain cells are in too great numbers and superfluous in a part, their action tending to restore the cell equilibrium.  The foreign cells do even more than this:  they themselves may be devoured by the growing cells of the tissue, seemingly being actuated by the same supreme idea of sacrifice which led Buddha to give himself to the tigress.