138 HEALTH AND DISEASE 



rubbing, scratching, or biting to relieve itching, or from the pressure of 

 harness. 



Having satisfied himself as to the existence of one or more of these 

 morbid conditions, the examiner is in a position to make a preliminary 

 diagnosis, possibly to form also a prognosis, and also to arrive at some 

 conclusion as to the cause of the disease and the principles of treatment. 



ETIOLOGY 



The causes of skin disease are numerous, and will naturally be a subject 

 of enquiry as soon as a diagnosis is arrived at. First, it will be evident 

 that the causes must be either general or local, but it would appear that 

 the two greatest dermatologists differed widely as to which of these two 

 was in operation. 



Hebra contends for the local origin of skin diseases, while Erasmus 

 Wilson adopts the reverse of that doctrine, and advocates the view that 

 skin diseases are, more commonly than not, the expression of some internal 

 derangement. The question is, however, only one of degree, as it is uni- 

 versally admitted that there are skin diseases both of local and constitutional 

 origin. 



A good idea of the causes which are generally in operation, as well as 

 example of the diseases they respectively induce, may be gained by 

 reference to the following succinct, and at the same time comprehensive 

 statement, made by Dr. Tilbury Fox in his work on skin diseases: 



1. Poisons of acute specific diseases. Examples, those of small-pox, 

 scarlatina, rubeola, &c. 



2. The circulation of special poisons: (a) of animal origin as syphilitic; 

 (&) medicinal substances, e.g. arsenic, belladonna, copaiba, nitrate of silver, 

 iodides, bromides; (c) dietetic, such as shell-fish, giving rise to urticaria, 

 roseola, erythema. 



3. Dietetic errors, as in wine-drinkers, high livers, non-vegetarians, &C., 

 leading to the increase of urea and uric acid in the blood. 



4. The tuberculous, scrofulous, and lymphatic dyscrasise, giving rise to 

 non-specific eruption as impetigo, acne. 



5. The gouty and rheumatic diathesis, as in lichen agrius. 



6. Altered and lowered nutrition, from such causes as bad living, 

 poverty, misery. 



7. The accumulation of excreta in the blood from suppression of natural 

 discharges, kidney disease, &c. 



8. Convalescence from severe and lowering affections, by which the 

 body is rendered much less able to resist disease. 



