If a small wad of cotton, soaked in strong ammonia, be placed on the skin and covered with a thimble and removed after two minutes, minute blisters of exudate slowly form at the spot.
The pain in an inflamed part is due to a number of factors, but chiefly to the increased pressure upon the sensory nerves caused by the exudate.

The pain varies so greatly in degree and character that parts which ordinarily have little sensation may become exquisitely painful when inflamed.

The pain is usually greater when the affected part is dense and unyielding, as the membranes around bones and teeth.
The pain is often intermittent, there being acute paroxysms synchronous with the pulse, this being due to momentary increase of pressure when more blood is forced into the part at each contraction of the heart.

The pain may also be due to the direct action of an injurious substance upon the sensory nerves, as in the case of the sting of an insect where the pain is immediate and most intense before the exudate has begun to appear.
When an inflamed area is examined, after twenty-four hours, by hardening the tissue in some of the fluids used for this purpose and cutting it into very thin slices by means of an instrument called a microtome, the microscope shows a series of changes which were not apparent on naked eye examination.

The texture is looser, due to the exudate which has dilated all the spaces in the tissue.