The usual explanation of the term is, an oversensitiveness to one thing or a few things. There may be a chronic idiosyncrasy from a chronic miasm and an acute idiosyncrasy from an acute miasm. There are acquired idiosyncrasies and idiosyncrasies that are born with a patient. …

The study of the idiosyncrasies is closely related to Homoeopathy. The usual explanation of the term is, an oversensitiveness to one thing or a few things. It does not apply to the general susceptibility in feeble constitutions where patients are susceptible to all things, over-susceptible and over-impressed by simple annoyances. In the old school idiosyncrasies relate to certain patients who are known in every practitioner’s practice as oversensitive.

One oversensitive cannot take Opium for his pains, because of the congestion it produces, because of dangerous symptoms; he is oversensitive to it and has complication from a very small dose even and the physician is compelled not to administer it. Another patient cannot tolerate Quinine in chills and fever; the primary action of Quinine makes him alarmingly sick; where another individual may take 15 grains. One who has an idiosyncrasy to Quinine cannot take –a state of quininism.

The homoeopath recognizes of wide range in susceptibility, including things that the allopath is not acquainted with. There may be a chronic idiosyncrasy from a chronic miasm and an acute idiosyncrasy from an acute miasm. There are certain individuals in every community that cannot ride in the country because of their susceptibility to hay fever; others cannot bear the smell of flowers in the room because of becoming sick; some will get sick from the smell of roses.

I have known a number of patients who became sick in this way. It is common enough, and the sickness is known by the name of rose cold or rose fever. I have a patient who cannot have dry lavender flowers in the house without coming down with coryza. She is disturbed by two or three things in this way, and will go looking about to see which one of those things is in the house. I had another patient who could not have peaches in the room without becoming sick; one of the symptoms that he had was diarrhoea.

This oversensibility is very important and it explains in a measure the susceptibility to the remedy that will cure. If an idiosyncrasy to the remedy is not present, the patient will not be susceptible enough to be cured. The state in which he becomes sensitive enough to a drug to cure him is very analogous to these idiosyncrasies above mentioned. Think what susceptibility man must have to the remedy that cures him, when it cures in the very high attenuations that we use.

There are acquired idiosyncrasies and idiosyncrasies that are born with a patient. Those that are congenital and those that come from poisons are most difficult. In Rhus tox. poisoning those that have once been affected by handling it are so sensitive to it that if they go within a quarter of a mile of the vine, though they cannot detect it with the nose, yet in a few days they will come down with a case of Rhus poisoning. A very high potency of Rhus will sometimes remove that susceptibility and a dose of Rhus c.m. or m.m. will often check the acute poisoning from Rhus: but if you find that the patient has been born with a sensitivity to Rhus, while Rhus may palliate a few times it will finally cease to help him.

When one is born with this sensitivity it is very tenacious and will sometimes persist, in spite of our best endeavours, to the end of life. If eradicated at all, it requires an antipsoric to get to the bottom of it. Hay fever is brought on in the fall and is supposed to be caused by the patient’s over-sensitiveness to irritants that develop about that time; sometimes it is attributed to the hay that is curing in the fields at that time, sometimes to the different weeds that grow up then.

Such patients have often been able to ferret out the thing that they are susceptible to. But psora is at the bottom of all these troubles. Patients getting up from typhoid fever have often idiosyncrasies, and the chronic miasms are responsible for these, just as psora is prior to the sore eyes from scarlet fever. Sequelae are miasmatic, they are simply the outcroppings of chronic miasms.

There are persons who are sensitive, not merely to one or a few things, but to all things; oversensitive to the high potencies, oversensitive in taste, oversensitive to light, and a great many other things. This is a constitutional state; the patient is born with it. There are persons in whom you will see the sensitiveness only when you go away from the plane of nutrition into the plane of dynamics.

You will see for instance patients who will sit at the table and crave common salt; want lots of salt upon their food, and never seem able to get just exactly what they need. They eat plenty of common salt and remain sick, growing thinner all the time. This is on the nutritive plane; the crude common salt is taken with the food. Now you administer the c.m. to such a patient, and it makes that patient sick, producing a violent aggravation. This is where a food sustains a curative relation upon a higher plane. We step out of the nutritive plane into the plane of dynamics, the plane of disease- causes and cure.

Take Calcarea as an instance. We see the allopath and crude medicine man give to certain babies, that are slow in forming bone and teeth and have open fontanelles, lime water in milk, and the more lime water he gives them the less bone they make. Here is a bone-salt inanition, a non-assimilation of lime. A dose of Calcarea very high will enable that child to take all the lime it needs from the food that it eats. The remedy given on the dynamic plane cause a digestion and assimilation of the lime naturally present in the food. You may feed lime in crude form, and no benefit ever come; the child goes on withering and emaciating.

In such non-assimilating patients the symptoms of Calcarea or Natrum mur. appear, calling the attention of the intelligent physician to the fact that the child needs Calcarea or Natrum mur. We know very well that we do not build bone with the c.m. potency of lime, it simply corrects internal disorder and causes the outward forms of the body to flow into order. The turning into order of the internal establishes the nutritive principle from the internal to the external. So that we can see the wider ranges the idiosyncrasy or susceptibility has in Homoeopathy.

Here we might undertake to coin a work, viz.:–homoeopathicity; what does it mean? Homoeopathicity is the relation between the homoeopathic remedy and the patient who has been cured. When the homoeopathic remedy has acted properly, when it has cured the patient, it has demonstrated that it was homoeopathically related to the case; so that the relation, when it was sustained, may be called the homoeopathicity, and it is demonstrated by administering the remedy.

It is true that we can have what would be called a normal homoeopathicity, a normal state, and that state exaggerated. That state exaggerated is where the patient is oversensitive to the curative remedy, and it not only establishes a curative relation, but before curing produces an exaggeration of the symptoms of the patient. A remedy demonstrates its similitude to a case by curing. Homoeopathic physicians use the word simillimum. The simillimum might be called that remedy that has cured the patient, but in advance of curing that case it is only what appears to be the most similar, a medicine cannot be called the simillimum until it has cured.

It is worthy of consideration to discover the difference between a poison taken upon the nutritive plane, that is, in crude substance, and a poison taken upon the dynamic plane. A poison upon the nutritive plane is usually not very deep, is more superficial, it relates more to external things, to the body and tissues, while the poison taken upon the dynamic plane may last a lifetime. The miasms are of such a character.

Poison taken upon the nutritive plane may bring about a life -long effect upon an individual, owing to susceptibility. The small doses of Arsenicum will establish an Arsenicum poisoning that will last a lifetime, but this is now where so deep as will be represented by the higher potencies of Arsenicum. To poison a patient with the higher potencies there is generally required something of susceptibility, while to poison patients upon the nutritive plane susceptibility is not required; any patient can be brought under the influence of a poison given upon the nutritive plane.

Here is another difference. Substances that are inert and substances that we can use as food on the nutritive plane may become poisonous upon the dynamic plane to those that are susceptible. So that there is no substance that may not be a poison in the higher and highest potencies. This gives us a distinction between crude and dynamic poisons that you will do well to think about.

Now from all this we are led to see that if there were no state of susceptibility, no such condition as idiosyncrasy, there could be no Homoeopathy. If there were no susceptibility, there would be no sickness and no need of Homoeopathy.

Susceptibility underlies all contagion and all cure. So that cause and cure, the cause of sickness and the cure of sickness, knock at the same door. They flow in the same way because of the immaterial or simple substance. All disease is in primitive substance, or first substance; all cure of disease must also be in simple substance. In olden times we used to think that all substances capable of extinguishing the vital force, or which overcome the vital force, were poisons; that in itself is a crude idea of a poison.

James Tyler Kent
James Tyler Kent (1849–1916) was an American physician. Prior to his involvement with homeopathy, Kent had practiced conventional medicine in St. Louis, Missouri. He discovered and "converted" to homeopathy as a result of his wife's recovery from a serious ailment using homeopathic methods.
In 1881, Kent accepted a position as professor of anatomy at the Homeopathic College of Missouri, an institution with which he remained affiliated until 1888. In 1890, Kent moved to Pennsylvania to take a position as Dean of Professors at the Post-Graduate Homeopathic Medical School of Philadelphia. In 1897 Kent published his magnum opus, Repertory of the Homœopathic Materia Medica. Kent moved to Chicago in 1903, where he taught at Hahnemann Medical College.