( 37 ) 
VI. PREVENTION. 
25. Measures Indicated. — It is a well-known fact that malaria lias been often eradicated 
from certain localities b)^ cultivation and drainage of the soil. Hence we arc justified in saying 
that the possibility of prevention has been demonstrated in some cases by experience. But 
cultivation and drainage are generally large and costly measures, and are often impossible. We 
propose now to examine whether the new observations regarding the propagation of the disease 
can suggest any cheaper, more precise, or more effective means of prevention. 
Since the disease is certainly conveyed by Anopheles, it is obvious — wlietlier tliis be the 
only mode of propagation or not— tliat measures taken against tiiese insects in any localit\ 
must assuredly be at least beneficial, even if they do not result in tiie entire extirpation of 
tlie malady in that place. 
King long ago pointed out [i] that if malarial fever be produced by gnats, prevention 
of the disease will consist in precautions against their bites by mosquito-nettings, window screens, 
and inunctions of the skin ; and in measures for the exclusion or destruction of tlie insects, 
such as screens of trees, smoke, fires and lights (in which he supposed they destroy themselves), 
and the draining of swamps and pools. Similar ideas liave occurred independently to other 
observers who have considered the gnat-theory. Nuttall gives [12] a summary of measures 
against gnats recommended hy various writer^ ^uch as draining or dumping tlie pools, or 
flushing them ; or agitating the water by wheels turned by wind-mills ; or tlie introduction of 
small fish ; or by the introduction of gnat-eating birds and dragon flies ; or by the use of 
fires, "lamp-traps," and so on, of inunctions to the skin, and of various " cidicicides," such as 
kerosene oil ; or by the plantation of water-absorbing trees. Celli and Casagrandi have recently 
reconsidered the subject, and have recorded a number of valuable experiments with various 
culicicides [26]. 
It will be observed that these measures can be resolved into two classes, namely :— 
(i.) Precautions against the bites of gnats. 
(2.) Measures for reducing their numbers. 
Of course, if malarial fever be communicated onlv b)' the bite of gnats, as there is now 
every reason to suppose [^paragraph 24], these measures will include the entire prophylaxis against 
the disease. If there be also some other method of propagation, other methods of prevention — the 
nature of which we cannot now indicate — will also be called for. 
Note also that we refer only to the prevention of infection, not to the prevention of the 
recurrences of fever, which often occur in a patient years after the primary infection, and which 
are not connected with the original infective causes at all. 
