URTICARIA. 



465 



distribution and limits, were it not that in a previous section we have 

 applied the title dermatitis to all the exudative diseases of the skin 

 without considering whether or not they are accompanied by genuine 

 inflammatory symptoms. We have also placed urticaria among the 

 acute inflammations, although there are cases in which patients have 

 Buffered for years from it. However, the disease has not been a 

 chronic one in such cases, but rather a series of acute relapses occur- 

 ring at very short intervals. The causes of nettle-rash are very varied. 

 Some of them we know, the rest are quite unknown. Urticaria has 

 been classified according to the different exciting agents which pro- 

 duce it 



1. Urticaria from External Irritation. Under this head come 

 all forms of nettle-rash arising from local irritation of the skin from 

 contact with stinging nettles, with the leaves of the rhus toxicoden- 

 dron, with the hairs of certain caterpillars, and with some of the mol- 

 lusca. It also includes the rash induced by the bites of fleas and 

 midges, and that caused in the skin of some people by scratching with 

 the finger-nails. 



2. Urticaria from Ingesta. This variety breaks out upon some 

 persons immediately after they have eaten strawberries, crabs, mus- 

 cles, mushrooms, or other unaccustomed food. It is quite hypothetical 

 to assume that in these cases an acrid material enters the blood and 

 upon reaching the skin occasions the irritation. It is very strange 

 that such food should only have this effect upon a few people, and that 

 in these it never fails to produce urticaria. The rash which we not un- 

 frequently see after the exhibition of large doses of balsam copaiba is 

 also included among the urticaria db ingestis. 



3. Urticaria febrilis oifebris urticata. The causes of this form 

 of the disease, which is accompanied by severe fever and gastric de- 

 rangement, and which greatly resembles the acute exanthemata in its 

 course, are unknown. 



4. Chronic Urticaria. The cause of this somewhat rare disease 

 is also obscure. It occasionally seems to depend upon hereditary pre- 

 disposition. 



5. There is a form of urticaria mentioned by Hebra, which is evi- 

 dently dependent upon uterine irritation, and which appears in some 

 women during pregnancy ; in others, during menstruation ; while in 

 others, again, it accompanies diseases of the womb, or follows the in- 

 troduction of pessaries. 



SYMPTOMS AND COURSE. The weals always rise from a base red- 

 dened by hyperaemia. They themselves, however, are often white 

 (urticaria alba s. porcellana), probably owing to compression of the 

 vessels of the papillae by the infiltration. Sometimes they are dis 



