PROPHYLAXY OF INFECTIOUS DISEASES. 
653 
of stagnant water in marshy regions. And, without knowing 
exactly the intimate cause of the disease, prophylaxy was car¬ 
ried out by drying off the marshes ; but it was always a costly 
and often impracticable operation. But numerous dangerous 
regions have been thus made healthy. 
Then, empirically, by a fortunate hazard it was learned that 
when the disease existed it could be cured by quinine. This 
was administered first in the shape of pulverized cinchona bark, 
then in that of salts, saltpetre or muriate of quinine. 
For a long time it was not known how quinine acted. Since 
then the parasitic nature of malaria has been recognized, and 
to-day it is well known that quinine acts in destroying the para¬ 
site, not under all its forms, or in every stage of its evolution ; 
it reaches it when it proliferates, when it gives birth to new 
legions of parasites. These beings, all in a condition to come 
to life, are destroyed by quinine. 
In times gone by it was believed that marshes were danger¬ 
ous from the emanations or effluvia arising from them which 
were transported by the air. To-day we know that it is not the 
air which carries the germs of the disease. Marshes are danger¬ 
ous because they are excellent media of culture for mosquitoes, 
and that it is by them that paludism is spread. This point 
well established, a new means of prophylaxy was indicated : it 
is to sterilize the marshes, to render them unfit for the culture 
of mosquitoes, when drainage cannot be applied. This method 
succeeds very well, when the stagnant waters do not cover too 
much space, by pouring on their surface a mixture of petrole 
and tar, which spreading in a thin layer over the water destroys 
the larvae of the mosquitoes by preventing them from breeding. 
The dangers from these insects are thus suppressed. 
Finally, when marshes cannot be drained or covered with 
petrole, one can yet protect himself from malaria in the regions 
most infested by using mosquito nets, especially during the 
night, the insect being nocturnal. With a good net one can 
cross the most infested countries without fear. This is an ex¬ 
ample which shows how simple prophylaxy is sometimes. 
