429 OK C6R-AL REEFS AS A CAUSE OF FEVER. 
healthy than others* but if this theory is correct, and my 
■chart not wrong, the islands of Haarlem, Hoorn, Engkhuyssen, 
and Leyden, must from the seeming absence of coral reefs 
be the most healthy. 
In anchoring vessels I would suppose that midway betwixt 
the islands and Batavia, and further out, on a parallel and 
near the island of Leyden are the two healthiest spots, and 
according to more than a dozen Masters of vessels, frequent 
traders betwixt this and Batavia, such are the healthiest spots. 
To anchor near Batavia would expose the crew to the effects 
of fresh water in a state of stagnation and filled with decom¬ 
posing animal and vegetable matter unaffected by tidal 
influence. And to anchor close to the islands of Onrust and 
Kuypers would be attended with still greater risk from the 
contiguous coral reefs. 
From my experience of the coral exposed situations near 
Singapore I have drawn this deduction—that during a change 
of a monsoon the locality subject to coral malaria is more 
unhealthy than at any other tim n . This applies to Batavia 
and its islands, for in both places the effect of the change 
will be evident in the production of greater fever, but when the 
rains have set in there will be a difference, for while in islands 
exposed to coral influence, the persistent heavy rains of a tro¬ 
pical clime will destroy the coral polyp, promote decomposi¬ 
tion and give rise to fever, such will not be so much the effect 
on localities suffering from fresh water swamps, for with them 
it is on the setting in of the dry monsoon or at the very com¬ 
mencement of the rainy season that fever is most prevalent. 
In this remark I am borne out by Dr Waitz whose Java ex¬ 
perience is of much weight—he says “ Agues during my 
stay at Samarang were more prevalent during the dry, than 
rainy season. 5 ' Count Hogendorp, lately Resident in Batavia, 
has found from calculations that one out of sixteen of the 
natives die annually, that the mortality during the rainy 
season is proportionally greater among old men and children 
under seven years, and on the contrary that the mortality 
during the dry season is more considerable among middle 
aged men. This in my opinion is in accordance with the 
well known fact that middle aged men are more obnoxious 
to fever than the aged or very young. 
In concluding this chapter and before taking leave of Ba¬ 
tavia harbour I would offer one suggestion. That if it is 
impossible to give up Onrust and other islands, the inha¬ 
bitants should if possible be protected from the influence of 
the coral malaria, and which can be done to a certain extent, 
by planting trees and encouraging the growth of mangroves 
