22 5 



to it, is also beyond doubt, as several authors have met with 

 frequent instances of its occurrence by descent. That so 

 few have recorded such cases is probably due to the fact 

 that in private practice only the most inveterate cases come 

 under notice, in which category hereditary eczema must 

 undoubtedly be placed. For example, a girl of sixteen was 

 placed under the care of Drs. Veiel (pere et fils) by her 

 father, a medical man. He himself, and his mother, as also 

 his second daughter, were sufferers from the complaint. 

 Similar examples might be multiplied. Eczema is observed 

 with special frequency in scrofulous and phthisical families. 1 

 Psoriasis is another well-known skin affection in which 

 heredity, if not its sole cause, plays a very prominent part, 

 and illustrates many of its peculiarities, as atavism, etc. No 

 rigid proof, says Weyl, can be brought at present that psori- 

 asis develops de novo> or can be produced mechanically or 

 chemically. Bazin regards it as a constitutional diathesis, 

 mainly hereditary, which is either of arthritic or herpetic 

 origin, and gives, as he imagines, the characteristic dif- 

 ferences of both forms. Others assume principally a single, 

 unknown, internal cause the dartrous diathesis. Weyl, 

 further, considers it probable that it is due to a functional 

 weakness of the nervous centre regulating the nutrition of 

 the skin, dependent on hereditary taint; this view is favoured 

 by the constant monotonous form of the efflorescence, and 

 its tendency to symmetrical development. The anatomical 

 process is merely the peripheral projection of the functional 

 central disturbance. According to Neumann, prurigo and 

 ichthyosis have never been found associated with psoriasis, 

 showing that all dermatoses may be combined, and that a 

 number of them exclude one another. 3 There can be no 



1 Dr. Th. Veiel (Ziemssen). 2 Dr. Weyl (Zeimssen). 



