This section is from the book "Materia Medica And Therapeutics: An Introduction to the National Treatment of Disease", by John Mitchell Bruce. Also available from Amazon: The pharmacology and therapeutics of the materia medica.
6. The trophic centres are amenable to impressions carried in by their afferent fibres, and such of these fibres as originate in the surface of the body are thoroughly accessible, and ready to convey any influence which we may impress upon them, such as extremes of heat and cold, by means of the cold bath or douche, stimulation by Mustard or Cantharides, and the direct battery current.
7. The metabolic activity of a part may be increased by certain local measures which are familiar to us, as friction and shampooing. The physiological effects of these local alteratives or local tonics are very powerful. Their action is complex, partly direct and partly reflex through the trophic nerves. They cause, first, dilatation of the local vessels, leading to increased circulation in the tissues; more rapid removal of the products of nutrition by the lymphatics and veins; and an actual exercise of the tissue elements, e.g. of the muscles, by well-arranged movements. No doubt these effects can be increased by the use of certain local circulatory stimulants, in the form of liniments of Ammonia, Alcohol, Chloroform, and the great group of Volatile Oils of the Turpentine and Camphor series. But, further, these local alteratives and tonics react upon nutrition generally, probably through the nervous system, and greatly stimulate it, improving the appetite and digestion, and rapidly causing an increase in the strength and the weight of the body, and thus become general tonics. The action of poultices, blisters, some forms of electricity, and other local applications, on the nutrition of deeper parts, which is known as counter-irritation, is discussed in chapter xv (. Therapeutical Processes Connected With The Surface Of The Body).
8. The surrounding temperature has a powerful effect upon nutrition. Heat and cold are universally recognised as being stimulating, enervating, relaxing, tonic or bracing, as the case may be. Water, in every form, from vapour to solid ice, is a convenient means of bringing any temperature that may be desired into contact with the tissues, whether directly or indirectly through the vessels and nerves. In other words, we possess, and have greatly elaborated, the means of affecting nutrition by baths and climate, the actions and uses of which are the subjects of balneology and climatology.
Medicines. We have made a further important discovery with respect to our influence over metabolism-that we can admit to the organs other than the normal constituents of the blood, and allow them to participate in the vital processes. Thus, if such foreign substances as Mercury or Arsenic be introduced into the blood, the muscular and other tissues will take them into their substance, just as they take up proteids, salts of lime, and water, and incorporate them in a loose chemical way, their own proper composition being essentially unaltered. By whatever channel they may be introduced into the blood, most of the active principles of the materia medica are carried, in the plasma to the tissues and organs, and are said to "act upon" or to "have a specific action" upon them. Thus, Iodine acts upon the glands, Bromine upon the brain, Potash on the heart, and so on. By this expression we mean that the medicines having reached an organ take part in the process of metabolism; that they become loosely incorporated with the anatomical elements of the part; that they form, either in these, or in the presence of these, certain chemical compounds with oxygen, different from the ordinary; that they are cast out again in the metabolic products, either unchanged or in a new chemical form; and that, in thus passing! through the organ and taking part in its activity, they have modified the force which it displays. Thus, Alcohol, in passing into muscle, becomes oxydised and converted into carbonic acid and water, and in the process of decomposition increases the force of muscular contraction. Alcohol is accordingly said to act specifically upon muscles. So with all tissues and organs: some incorporate from the blood one substance, some another. Just as the life-processes of the various tissues and organs differ from each other, so will some select or be acted on by some principles, others by other principles. Gland protoplasm is acted upon by Iodine, nervous protoplasm by Bromine, muscle protoplasm by Potash, red corpuscle protoplasm by Iron, and so on.
Here it is necessary to offer a word of caution. The expression "action" of a medicine is generally used in a much wider sense than that just indicated. When we say that a given therapeutical substance acts upon "an organ," we do not always mean that it acts upon the protoplasm of that organ. When we say that alcohol acts upon the skin, flushing it and increasing its heat and secretion, we do not imply that alcohol is decomposed by the connective tissue-cells of the skin. An organ possesses not only active protoplasmic cells but vessels and nerves; and a vast number of the effects of drugs upon organs are due, as we shall see in subsequent chapters, to their action upon the vessels and the nerves that supply these organs. Ultimately, of course, all drugs do act upon protoplasm in some form, on the protoplasm of muscular tissue, of nerve-ganglia, of the walls of blood-vessels, or of the cells of the nerve-centres which regulate the vessels. But for practical purposes it is highly important to keep the action of drugs upon the protoplasm of an organ quite distinct from their action upon the organ through its nerves or its blood supply.
Alteratives.-The subject of metabolism introduces us to a term applied to certain drugs, namely, alteratives. This word, like many other terms in therapeutics, never had an exact application, and therefore defies correct definition. Still, it is retained as a useful word, and its meaning may be discussed if it cannot be defined. We have seen that we can increase the amount of work done by an organ in several ways, through food, air, local stimulation, etc., which make it build up and break down more actively both its pabulum, the lymph, and its own proper elements: which, in one word, exercise it. Certain medicinal substances also are found to increase metabolism, the chief of which are Mercury and Iodine, Phosphorus, Antimony, and Arsenic, Sulphur or Sulphides, and certain doubtful vegetable agents, such as Sarsa and Guaiacum. The particular way in which each of these drugs increases tissue waste is given under its own head, as far as it is known. It naturally occurs to us, that the action of these medicines is another form of exercise of the tissues. When Mercury and Iodine, for example, have entered into combination with living protoplasm, and been again disengaged or thrown out of combination with it in the metabolic products, they have made it do a certain amount of work: and to a corresponding extent they have effected a change and a renewal of its proper molecules; they have hastened its nutrition; their action may be said to be alterative. We find that an essential condition of the success of alterative drugs is a free supply of the normal sources of metabolism, food and air, just as it is of physical exercise, that the constructive part may keep pace with the destructive part of metabolism. If food and air fail, the health rapidly breaks down, the body wastes, and death may result. Possessing a powerful and peculiar action like this, these medicinal agents fully deserve the name of alteratives, and any method of treatment which may be founded upon their action is incomplete unless it include abundant feeding and fresh air.