Let us now consider the hereditary behavior of some of the commoner diseases, including those which, while not fatal or apt to incapacitate a person, nevertheless interfere with his happiness. Knowledge in this field is less precise, although the general teaching is not less clear. As a source of information I rely chiefly on the records of health and other characteristics furnished for over 200 families by members of the families concerned. These are largely representatives of professional circles, but include also farmers and people in commercial life.
In the pedigrees that follow nothing is more evident than that usually specific diseases are not inherited but only a condition of liability or non-resistance to a particular class of disease. Often an entire organ-complex is thus non-resistant.
A good example of inheritance of general weakness in an organ is sometimes found in the case of the mucous membranes.
In the N family the principal diseases to which there is liability are located in the mucous membranes of nose, throat, ear and bronchia. (B 3.)
Fit and Unfit Matings
In the D family the center os susceptibility is more specific, being nearly confined to the nose and throat. (B 4.)
In the E family the center of weakness is the ear. (B 5.)
In the N family the trouble seems to spread from the throat. (B 6.)
In the M family the susceptibility is more nearly confined to the lungs. (B 7.)
In another family the [italics]skin[end italics] seems to be the weak organ, boils and eczema are common. (B 1.) In still another tubercles and absesses seem to be associated. (B 2.)
In other families the kidneys will be the seat of incidence. In one it will take the form of Bright's Disease and dropsy (B 9): in another uremic poisoning and "rheumatism." (B 8.)
Heart disease is a very general term; there is no doubt its inheritance although the precise nature of the weakness is varied. (C 1, 2.)
Nervous disease re-appears as paralysis, neurasthenia, nervousness, headaches and stomach trouble, and migraine appears in successive generations. (C 3, 10; D 2.)