VIII. Circumstances by which the Fluids, that are effused by the retrograde Motions of the absorbent Vessels, are distinguished.

1.  We frequently observe an unusual quantity of mucus or other fluids in some diseases, although the action of the glands, by which those fluids are separated from the blood, is not unusually increased; but when the power of absorption alone is diminished.  Thus the catarrhal humour from the nostrils of some, who ride in frosty weather; and the tears, which run down the cheeks of those, who have an obstruction of the puncta lacrymalia; and the ichor of those phagedenic ulcers, which are not attended with inflammation, are all instances of this circumstance.

These fluids however are easily distinguished from others by their abounding in ammoniacal or muriatic salts; whence they inflame the circumjacent skin:  thus in the catarrh the upper lip becomes red and swelled from the acrimony of the mucus, and patients complain of the saltness of its taste.  The eyes and cheeks are red with the corrosive tears, and the ichor of some herpetic eruptions erodes far and wide the contiguous parts, and is pungently salt to the taste, as some patients have informed me.

Whilst, on the contrary, those fluids, which are effused by the retrograde action of the lymphatics, are for the most part mild and innocent; as water, chyle, and the natural mucus:  or they take their properties from the materials previously absorbed, as in the coloured or vinous urine, or that scented with asparagus, described before.

2.  Whenever the secretion of any fluid is increased, there is at the same time an increased heat in the part; for the secreted fluid, as the bile, did not previously exist in the mass of blood, but a new combination is produced in the gland.  Now as solutions are attended with cold, so combinations are attended with heat; and it is probable the sum of the heat given out by all the secreted fluids of animal bodies may be the cause of their general heat above that of the atmosphere.

Hence the fluids derived from increased secretions are readily distinguished from those originating from the retrograde motions of the lymphatics:  thus an increase of heat either in the diseased parts, or diffused over the whole body, is perceptible, when copious bilious stools are consequent to an inflamed liver; or a copious mucous salivation from the inflammatory angina.

3.  When any secreted fluid is produced in an unusual quantity, and at the same time the power of absorption is increased in equal proportion, not only the heat of the gland becomes more intense, but the secreted fluid becomes thicker and milder, its thinner and saline parts being re-absorbed:  and these are distinguishable both by their greater consistence, and by their heat, from the fluids, which are effused by the retrograde motions of the lymphatics; as is observable towards the termination of gonorrhoea, catarrh, chincough, and in those ulcers, which are said to abound with laudable pus.