PROPHYLAXIS. 667 



Other points in individual prophylaxis are, first, 

 the application of ethereal oils (clove oil, oil of 

 pennyroyal) to the exposed skin, and, second, the 

 use of mosquito netting. 



The important practices for general prophylaxis General 

 are the following: 1. The draining of swampy J 

 places and of pools of water where anopheles may 

 deposit its eggs. This in many instances manifest- 

 ly can not be accomplished. 2. Covering pools of 

 water with petroleum. This is to a degree success- 

 ful. Every square meter requires 0.5 liter of pe- 

 troleum (Kerschbaumer), and the oil must be 

 added fresh every seven or eight days. The layer 

 of oil excludes the air from the larval mosquitoes 

 and they drown. If fresh oil is not added occa- 

 sionally new eggs may hatch. 3. Koch's method of 

 extermination of malaria. This consists of the 

 searching out of all cases of malaria and the de- 

 struction of the parasites by appropriate quinin 

 treatment. Koch practiced this method in an in- 

 fected locality of New Guinea and in a relatively 

 short time freed it of malaria. If all the plas.modia 

 in a community are destroyed the disease can not 

 again become endemic unless it is introduced from, 

 without or unless infected mosquitoes are imported. 

 Manifestly this method must be practiced on an ex- 

 tensive scale in order to render it permanently 

 successful. It seems to have been demonstrated, 

 however, that the number of cases in any given 

 locality may be materially decreased by pursu- 

 ing it. 



So far as is known, susceptibility to malaria is immunity. 

 universal. The belief is very general that one 

 attack of malaria not only does not protect against 

 reinfection, but even predisposes to it. Two facts. 



