This section is from the book "A Compend Of The Principles Of Homoeopathy", by William Boericke. Also available from Amazon: A Compend of the Principles of Homoeopathy as Taught by Hahnemann.
The greatest evil of these miasms, is that they are made organic and rendered permanent by heredity. It is this fact of heredity and the pollution of the vital fluids * entailed thereby that modifies not only the course of acute diseases, but establishes and makes a permanent field for chronic diseases. This hereditary gift and this organized field give rise to certain bodily constitutions and certain dyscrasic conditions. Acute diseases and possibly the action of remedies run their course in the track marked out by these bodily constitutions, which again are largely modified by the latent psoric taint.
Every practitioner of experience arrives sooner or later at this fact - namely, that in order to get a true and practical understanding of diseases, the ground, the human organization modified more or less by heredity, upon which ground diseases feed, and which is the battlefield of the malignant forces of disease from without combining with the impurities within, the character of this ground must be studied; for, according to its composition, it will certainly modify one way or another the course of diseases that from time to time invade it. The presence of this modifying something - this perturbing and yet determining factor - this psoric taint, was recognized by Hahnemann. His facts are true; his theory, true or not, is, nevertheless, an admirable working theory, leading to remarkable, successful results.
* "The vaccinated syphilis of one organism passing into another, may not manifest itself by eruption, or chancre or visible syphilitic taint at all, but may fall upon the nervous life and be a raging and unappeasable lust in afterlife". - J. J. Garth Wilkinson.