700 



DR C. HUNTER STEWART ON THE 



fact already poiDted out that the upper 3 or 4 feet is made soil, and not at all similar to 

 the natural soil below. The increase with depth is seen in the following comparison 

 between the 6 feet and 12 feet determinations at the Infirmary and the 3 feet and 6 feet 

 determinations at Heriot's Hospital Grounds. 



Infirmary J 



Grounds, | , ~ 



Heriot's ( 3 „ 

 Hospital < 

 Grounds, ( 6 „ 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Jan. 



Feb. 



Mar. 



Apr. 



May. 



June. 



July. 



9-85 

 15-99 



10-7 

 16-0 



13-8 

 171 





















6 

 8-3 



6-6 



8-04 



7-4 

 8-5 



3-1 

 3-9 



3-3 

 3-2 



3-5 



4-06 



4-1 

 4-56 



3-6 



3-9 



4-0 



4-5 



3-7 



4-1 



4-6 



4-9 



5-3 



6-4 



The importance of the role played by the soil in the etiology of disease, which has 

 long been insisted on by Pettenkofer and the Munich School, has been emphasised by 

 the elaborate investigation and report made by Dr Ballard to the Local Government 

 Board in 1887 on the causation of summer diarrhoea. He attributes its epidemic occur- 

 rence to some decomposition taking place in organically contaminated soil under the 

 influence of micro-organisms at the depth of about 4 feet. The marked feature in these 

 epidemics is the great and sudden increase in the number of cases at the end of July and 

 beginning of August, at which time he found the underground temperature at a depth of 

 4 feet to be at its maximum. This sudden rise is followed by a comparatively slow 

 decline. A reference to the curves in the tables accompanying this paper will show that 

 the carbonic acid in the ground-air reaches suddenly its maximum amount at the same 

 period, and that its decline is similarly slow. Since carbonic acid is a product of bacterial 

 action on organic matter, it is evident that the upper reaches of the soil are biologically 

 most active at the time when summer diarrhoea attains its maximum intensit}^. 



As showing that the amount of carbonic acid in ground-air is to some extent a 

 measure of organic matter present in the soil, I append the following experiments made 

 in January ; — 



Averagely Pure Soil, 3 Feet. Disused Burying-Ground 3 Feet. 



Organic Nitrogen, . . . 065 per cent. ... 0136 per cent. 



Carbonic Acid in Ground-Air, . 3 - 6 c.c. per litre. ... 13"5 c.e. per litre. 





