314 Proceedings of Royal Society of Edinburgh. [sess. 
magnetic dip (isoclinal lines).* I tliink that this theory is well 
worthy of study. 
I must reserve for the present any further elaboration of the 
subject of this paper, hoping to be able to resume it at a future 
time. 
My thanks are due to Dr John Murray for permission to use 
Plate No. XIV., and to Dr Buchan, Dr Woodhead, and Mr J. G. 
Bartholomew for some assistance and advice. My indebtedness to 
authors are acknowledged in the text. 
EXPLANATION OF PLATES. 
Plate I. 
Chart of the world showing the area of endemic and epidemic malaria. The 
colouring depicts, as nearly as possible on such a small scale, the severity of 
the disease in various regions. 
Plate II. 
Chart showing the endemic habitat of Dengue and also the area of its 
epidemic spread. The darker colour shows where the disease is endemic. 
Plate III. 
Chart showing — I. The native habitat of Asiatic cholera ; II. The area over 
which pandemic waves of cholera have spread ; III. Regions to which cholera 
has never penetrated ; IV. Districts from which no information is obtainable. 
Plate IV. 
Chart showing — A, the area over which yellow fever is endemic and epi- 
demic ; B, the districts in which Oriental boils or sores are endemic ; C, the 
limited areas in Africa and in the Mauritius in which, so far as yet known, 
endemic hsematuria occurs. 
Plate V. 
Chart showing-— A, the areas in which Beri-Beri is met with; B, the districts 
which have been visited by Oriental plague during recent years. 
Plate VI. 
Chart showing the geographical distribution of tropical dysentery, its 
prevalence being indicated, as far as possible, in the colouring. Its epidemic 
occurrence in non-tropical countries is also shown. 
Plate VII. 
Chart showing the distribution of leprosy at the present time, its greatest 
prevalence being distinguished by the colour. 
Plate VIII. 
Chart showing — A, the geographical distribution of Yaws ; B, the region 
where the Fungus disease of India is met with. 
* The Milroy Lectures. Lawson, 1888. 
