288 Proceedings of Royal Society of Edinburgh. [sess. 
persons suffering from the disease, even should they he almost con- 
valescent. It is said that should a thunderstorm occur, severe 
symptoms are immediately manifested in persons suffering from the 
disease, or a relapse occurs in the apparently convalescent. 
Yellow fever poison clings to the ground, and its diffusion may 
be barred by streams, walls, and, some say, by much travelled 
thoroughfares, and it does not appear that the water-supply of 
cities aids its spread. Its period of incubation is variable, and may 
be said to be between twenty hours and several weeks ; this varies 
in different epidemics, and the most common period of incubation 
Is from twenty to one hundred hours. 
Preventive inoculations are now being largely practised against 
yellow fever with very great success, and there seems to be every 
reason to hope that at last a method of preventing the disease will 
be firmly established, although up to the present its true origin has 
escaped scientific inquiry. 
The disease may be spread by fomites, and its toxic power 
retained for very long periods. 
Y. Oriental Sore or Boil. 
(See Plate IY. B.) 
Synon . — Aleppo Evil; Mycosis Cutis Chronica (Carter); Lupus 
Endemicus (Lewis and Cunningham) ; Oriental Sore (Fox) ; 
Mooltan and Biscara Boil ; Date Disease ; Caneotica ; Liblib ; 
Yemen and Cochin-China Sores; Scinde Boil; Parangi; Maid’ Alep ; 
Fr. Bouton d’Alep ; Ger. Yeule von Alep. 
Definition . — An indurated, indolent, and very intractable sore ; 
papular in the early, encrusted or fungating in the advanced stages ; 
spreading by ulceration of the skin, single or multiple ; and often 
occupying extensive surfaces of the exposed parts of the body, such 
as the face, neck, and extremities. It is capable, if innoculated, of 
reproducing the disease, and it also affects dogs and horses. 
Geographical Distribution . — In Europe the boil is met with in 
Crete, in Cyprus, and in the Crimea. In Africa there is a consider- 
able area in Morocco, on the banks of the Muluia, where the 
disease abounds, as it does also in numerous oases of the Algerian 
desert and in the Tunisian Sahara. It is occasionally met with in 
