672 PROCEEDINGS OF SECTION H. 
whatever may be the case about the conditions necessary for the 
germination of the bacillus, investigated by Eberth and Gaffky. 
The alternative has been to lay stress on the varying degree of 
dryness and dampness of the soil as being the real determining 
cause of the seasonal variations. This is the well-known 
Grundwasser theory, elaborated chiefly by the Munich school 
of epidemiologists, the position taken being that the prevalence 
ot typhoid in a locality, at different periods, varies inversely with 
the high or low level of the subsoil water. This relation seems 
to be well established, at least for some places, whatever be the 
explanation. But the level of the subsoil water must depend on 
the amount of rainfall at the locality, or on the level of the water 
of a river on whose banks a town is built. In most places it 
will depend on the rainfall ; andif the Grundwasser theory is 
correct, a maximum prevalence of typhoid should fall, not only in 
the dry season of the year, but epidemic periods should especially 
be in dry years. Facts in support of both of these points were 
collected by Prof. Soyka (loc. cit). 
Another general condition that might be supposed to be of 
importance, at least on the supposition that the disease may be 
caused by emanations from the soil, is variation in the barometric 
pressure. Where that pressure is low, exhalations will rise more 
easily, and be more widely distributed. 
The only other meteorological condition which has been 
supposed to have influence on the spread of epidemic disease is 
the presence or absence of ozone in the atmosphere. That, how- 
ever, has not been made the subject of observation continuously 
enough, or on a sutliciently large scale, to allow of very reliable 
conclusions being based on it, and here there are no useful data 
available. 
Rather contradictory opinions have been expressed as to the 
influence of meteorological conditions in determining the degree 
of prevalence of typhoid in Melbourne. There has also been 
some confusion, I think, caused by combining the terms “hot” 
and “dry,” descriptive of the general peculiarities of particular 
seasons as compared with others spoken of cool and moist. Often, 
too, I fear that the opinions expressed have been based merely on 
general impressions, and not on adequate or carefully-sifted 
statistical data. As to the influence of temperature by itself, 
what has been already said seems to be sufficient to show that it 
can have little importance. Ii, in different towns in Europe, in 
about the same latitude, typhoid is most prevalent in one during 
the autumn, and in another in the depth of winter, it is hardly 
conceivable that a difference of one or two degrees in the average 
temperature of the summer months, or of the year, should be the 
determining cause of the marked fluctuations found in the 
mortality from it in Melbourne in successive years. Heat as a. 
factor per se may therefore, I think, be disregarded. 
