PROCEEDINGS OF SECTION H. 667 
breaks is generally supposed to be due chiefly to the accumula- 
tion, in the intervals, of susceptible persons. It is doubtful, 
however, whether this supplies a full explanation in the case, 
even, of diseases of the type referred to. And where we have to 
deal with a disease like typhoid, which attacks persons of all 
ages, without showing any preference for children, such an 
explanation is clearly quite inadequate. 
About three years ago (Australian Medical Journal, January, 
1887) I pointed out that through a long series of years there had 
been a very marked and regular periodicity in the rise and decline 
of the mortality from typhoid in Melbourne, severe outbreaks 
being separated by intervals of about four years. I was not 
aware at that time that any such peculiarity had previously been 
noted, and no mention is made of it by Hirsch in his “‘ Handbook 
of Geographical and Historical Pathology.” But im a lecture by 
Dr. Port, delivered in Munich in 1880, I find the following state- 
ment (Zur Aetiologie der Infections-Krankheiten, p. 129)—‘‘ In 
each of our barracks there appears to be a certain regular succes- 
- sion of good and bad years, which as different for the several 
barracks. For the new barrack on the Isar, about which recol- 
lections go somewhat further back than about the others, Dr. 
Anderl believes that a five-yearly cycle must be fixed.” The 
regular succession, at intervals of about four years, of periods of 
rise and fall in the typhoid mortality of Melbourne, through a 
long series of years, is very clearly shown in the accompanying 
chart. On the same chart I have placed the curves of typhoid 
mortality for Sydney, unfortunately for a shorter period, but for 
as long a time as full information is obtainable. In the case of 
Sydney there are indications of periodicity, though not sufficiently 
distinct to ground any argument on. The remarkable parallelism 
of the curves for the two cities, during the period 1876-82, is 
suggestive of the operation of general conditions, of wide-reaching 
nature, perhaps resembling those which permit the spread of 
cholera, at particular periods, over great parts of the world. In 
more recent years there has been approach to parallelism in the 
curves for the two cities. In the last three years, too, there has 
not been the previously observed regularity of the curves for 
Melbourne. There has not been the anticipated decline after the 
acme reached in 1887, and instead of a continued fall in 1889 
there has been a second rise. This irregularity may possibly be 
accounted for bya quite unprecedented amountof breaking-upof the 
surface in almost all parts of the metropolis, not only for building 
purposes, but in the construction of tramways, laying of wood- 
paving, &c. Outbreaks of typhoid have been supposed to be 
connected with similar causes in other cities. But supposing 
there is such periodicity of recurrence as is shown in the chart, 
there must be account taken of it in any inquiry into the general 
causation of the disease. 
