The exact nature of their effect on the nervous system has not been made out. Their action on the skin and epithelial cells of the lungs seems to be that of causing fatty degeneration.

Fatty degeneration of the liver occurs also in poisoning by salts of silver.

Mercury has a peculiar power of breaking up newly deposited fibrin and of causing disorganization of syphilitic deposits. Iodine, iodides, and probably also chlorides, appear to act on the lymphatic system and promote absorption: their action is specially well marked in cases of glandular enlargement.

Uses. In general mal-nutrition without definite symptoms, mercurials, taraxacum, and nitrohydrochloric acid are used and are especially indicated where the liver is suspected to be in fault, as where there are symptoms of biliousness, and also where oxalates and urates are found abundantly in the urine.

In gout, potash and colchicum are used. Phosphorus and arsenic are employed in nervous debility: and they as well as antimony are serviceable in neuralgia, chorea, and other nervous diseases.

In diseases of the skin, arsenic is chiefly employed.

In diseases of the respiratory organs, antimony is very serviceable when the attack is acute; and arsenic is most valuable in some chronic conditions, especially in chronic consolidation, where it probably acts by producing fatty degeneration and softening of the effusion, so that it is either absorbed or expectorated.

Mercury is employed specially to break up deposits of lymph and to prevent adhesions, as in iritis and pericarditis; and is also used and is most serviceable in the treatment of syphilis. It is most generally employed in the secondary stage of this disease: in the third stage it is either given along with, or entirely replaced by the use of, iodides.

Antipyretics, Febrifuges.

These are remedies which reduce the temperature of the body in fever. They act much more powerfully when the temperature is abnormally high than when it is normal.

The constant temperature of warm-blooded animals depends upon the maintenance of a proper balance between the amount of heat generated in the body, chiefly by oxidation, and on the amount given off to the surrounding medium-air or water. The heat is chiefly generated in the muscles and glands. It is chiefly given off by the skin, although some is also lost by the lungs, etc.

A little heat, but not much, may be given off by radiation alone. The power of dry air to take up heat is very slight, and so the skin is not much cooled, and very little sensation of cold is felt at temperatures much below 0° if the air is both still and dry. If the air be moist its capacity for heat is much greater, and the loss of heat from the skin being much more rapid, a person may actually feel the weather colder at 4° F. than at -40° F., the air being still in both cases. If air, either dry or moist, is in motion, so that fresh portions of it come successively into contact with the skin, the loss of heat is much more rapid, and a little

wind will render even dry air unbearably cold at a temperature which would be quite supportable if the air were still.

It is to be observed that during sleep the action of the vaso-motor centre is less, the vessels of the surface dilate, and loss of heat, with danger of consequent chill, takes place more rapidly. For the effects of local chill to the surface, vide Rossbach's experiments (p. 225).

Antipyretics may be divided into two great classes: those which lessen the production of heat, and those which increase the loss of heat; and these again may be subdivided as shown in the following table::

The mode of action of those which affect the blood and tissues themselves has already been considered tolerably fully under the head of "Oxidation of Protoplasm" (p. 77). They appear simply to diminish the temperature by lessening oxidation. The mode of action of antipyretics which produce their effect through the circulation, has not been investigated in detail with satisfactory exactitude, but it is supposed that by lessening the rapidity of the circulation through those parts of the body in which the increased tissue change is taking place, the temperature is reduced.

Blisters will have this effect locally by causing contraction of the vessels in the inflamed part, as already described under the head of Counter-irritants (p. 303).

Antipyretics, which increase the loss of heat, may do so by causing greater dilatation of the vessels of the skin, and thus allowing a quicker radiation of heat from the body; (2) by augmenting the secretion of sweat: and thus carrying off heat by means of evaporation; or (3) they may actually remove warmth from the body, as cold baths, cold affusion, cold sponging, wet packing, cold enemata, or ice to the surface.

Uses.-Antipyretics are used to lower the temperature when it has risen above the normal, whatever be the cause. A high temperature may be produced simply by prolonged exposure to heat. This exposure, and the rise in temperature it occasions, seems to induce increased tissue change, and this increase of the tissue change will keep up a febrile temperature, even after the external temperature has fallen. Such thermal fever is found in warm climates, and in it quinine injected subcutaneously seems to be very efficient.

A high temperature may also occur from specific fevers, as typhus, typhoid, scarlet fever, measles, and acute rheumatism. The most rapid and powerful antipyretic in such cases is the application of cold by bathing, or sponging; and probably next come large doses of quinine or salicylate of soda. In typhoid fever, salicylate of soda does not seem to act so rapidly as it does in acute rheumatism.

Venesection, though formerly the antipyretic which was chiefly relied upon, has now fallen to a great extent out of use-this is probably from its having been very much abused.

In persons suffering from acute inflammation of the lungs or bronchi, where the amount of lung tissue which remains sound is insufficient to aërate the whole mass of blood, and the patient is becoming livid, small bleedings are serviceable, not only relieving the breathing, but lessening delirium which may be present.

Venesection lowers the temperature for a short time, but it soon rises again in many cases, so that bleeding alone is by no means a powerful antipyretic,1 unless the quantity of blood abstracted be so great as probably to injure the patient seriously; yet in combination with other antipyretics it may sometimes be of very great service.

Local bleeding by leeches or by wet cupping sometimes gives very great relief, lessening both local inflammation and the general symptomatic fever consequent upon it, in pneumonia, pleurisy, pericarditis, peritonitis, etc. In such cases blisters may be used to diminish the local inflammation, and thus aid the action of other antipyretics.

Vascular antipyretics, such as aconite and digitalis, also seem to be of more service in symptomatic fever than they are in specific fevers.

Purgatives take an intermediate place between antipyretics which lessen the production of heat by acting on the tissues, and those which act on the circulation. They diminish the force of the circulation, and

1 Wunderlich's Medical Thermometry, pp. 118, 134, 378, New Sydenham Society's edition.

may in this way lessen the production of heat. It is not impossible also, however, although this is a point on which we have not sufficient information, that they may do so by removing from the body substances whose effect when present in the circulation or tissues would be to maintain the high temperature.

Amongst antipyretics which increase the loss of heat we have: first, alcohol, which is included also in the former list of those which lessen the production of heat, for it appears to act in both ways, both diminishing oxidation and also increasing the loss of heat. It does this by dilating the vessels of the skin and allowing free radiation from the surface, and also by the cooling effect of evaporation of the sweat, although its action as a sudorific is not very marked.

We have also the whole class of sudorifics. One of the most useful of these in checking a febrile condition just at its onset is a dose of compound ipecacuanha powder, or Dover's powder, which has now, to a great extent, taken the place of the older remedy, having a somewhat similar action, viz., antimonial powder, or James's powder.

Another mixture in great favor is acetate of ammonia and spirits of nitrous ether. The most powerful, however, of all remedies which increase the loss of heat are the application of cold water or ice.

CHAPTER XV.

ACTION OF DRUGS ON EXCRETION.

Action of Drugs on the Kidneys.

The kidney has a twofold office. It has (1) to regulate the amount of water in the body under various conditions; (2) to remove the products of tissue waste. These products must be removed in a state of solution from the part of the kidney where they are excreted, and yet sometimes provision must be made for the water, by which they are washed out, being retained in the body. The urine in mammals and amphibia is liquid; in birds and reptiles it is semi-fluid or solid, yet the solid constituents are removed in solution from the urinary tubules, and the water in which they are dissolved is afterwards absorbed. We may say then that the kidney has not only a twofold, but a threefold action:-1st, the excretion of waste products; 2dly, a provision for the removal of excessive water; and 3dly, an arrangement for the retention of water in the body by its re-absorption, after it has washed out the waste products. On looking at the kidney we find three structures which seem to be connected with these three functions, viz.: (1) convoluted tubules with epithelial cells, which in all probability are the chief

structures for excreting waste products; (2) the Malpighian corpuscles for excreting water along with some solids, and (3) usually one or more constrictions in the tubule which may serve the purpose of preventing too rapid exit of the water, and thus allow time for its re-absorption in cases where its retention is desirable, as for example on a hot day and when the supply of drinking-water is very limited.

The process of secretion in the kidney was regarded by Bowman as consisting of the filtration of water from the vessels of the glomeruli into the tubules, and the excretion of waste products by the epithelium lining the tubules. Ludwig, however, came to look upon it rather as a process of filtration and re-absorption; a dilute solution of urea and salt being according to him poured out from the Malpighian corpuscles and gradually concentrated by the absorption of water in its passage along the tubules. This theory had so many facts in its favor that it was for a good while exclusively adopted, but latterly Heidenhain in an admirable series of experiments has shown that such substances as indigo are

FIG. 112.-Diagram showing the form of the urinary tubules in different classes of animals, after Hüfner. I. Fish. 2. Frog. 3. Tortoise. 4. Bird. 5. Mammal. The letters have the same signification in each. a. Capsule of the glomerulus. b. Convoluted tubule. c. Loop. d. Collecting tubule. u in 2 indicates the transverse section of the ureter.

certainly excreted by the epithelium of the tubules. At the same time Hüfner has shown by a comparison of the structure of the kidney in fishes, frogs, tortoises, birds and mammals, that the form of the tubules closely agrees with that required for the re-absorption of water in each

case.

Fishes have a low blood-pressure, and so the resistance in the kidney requires to be small in order to allow of the secretion of urine. Living as they do in water, they do not require any apparatus for its retention in the body. In them therefore the tubule is short and wide, and destitute of any constriction which would retard the outflow of fluid. In frogs there must be ample provision for the retention of water in the