PROCEEDINGS OF SECTION H. 671 
most cases of localised outbreaks of typhoid in this city, there 
existed marked and special defects of drainage, and very often 
underground drains, which are too frequently badly laid, badly 
tapped, and with no means of ventilation, except by the inlets 
from yards or houses. 
It is unnecessary to reiterate the proofs, so often supplied, that 
the introduction of an efiicient system of underground drainage 
has almost with certainty the effect of lessening rapidly the 
prevalence of typhoid in a town or city. The effect may be 
produced in more ways than one: in some cases, perhaps, by 
diminished liability to contamination of the water supply ; but in 
the case of large towns, with water conveyed by pipes from some 
distant source, the probability rather is that the great and 
continuous effect is due to purification of the soil, and consequent 
prevention of the formation and escape of foul emanations. 
But although it may be sufficient, for some purposes or on 
some occasions, to determine that the medium for conveying the 
poison was milk, water, or air, there are other points in connec- 
tion with the natural history of the disease which any such 
decision still leaves unsettled. Among the most important of 
these is that which concerns the periodical recurrence of the 
disease, whether it be the annual rise and fall, or the fluctuations 
in the degree of prevalence, as observed through a series of years. 
The annual fluctuations seem to occur in all parts of the world, 
and the rule is for the disease to become increasingly frequent 
during the late summer and autumn months. The tendency has 
always been to account for this mainly by the rise of temperature, 
and especially by the increased heat of the soil. This view is 
considered to derive support from the discovery of the specific 
bacillus, and the determination of the degree of heat at which 
spore-formation takes place. This might be a fairly satisfactory 
explanation if it were always true that the maximum prevalence 
is in the late summer and early autumn. But, as a matter of 
fact, this period of maximum intensity is not the same in all 
countries, even under approximately similar latitudes. Taking 
the continent of Europe, for instance, it has been found by Prof. 
J. Soyka (Archiv. f. Hygiene, 1887, quoted in Schundts Jahrbiicher, 
Bd. 220, No. 2) that the maximum of mortality falls on the 
months of August to October in Berlin, Neufchatel, Lausanne, 
Breslau, Frankfort-on-the-Main; September to November in 
Hanover, Basel, Paris; October to January in Bern; JVovember 
to March in Munich ; January to March in Prague; March to 
May im Vienna. It is clear, therefore, that other considerations 
besides mere temperature of air and soil have to be taken into 
account. When it is also mentioned that in Christiana, with its 
severe winters, the maximum prevalence of typhoid falls in the 
months from November to January, it might be said, further, 
that mere temperature by itself is of very slight importance, 
