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of crude kerosene on larvae of Stegomyia fasciata, five larvae, in eacli 

 case, were enclosed in test-tubes containing respectively, a natural 

 medium, tap water, containing a fair amount organic matter, and 

 distilled water. A layer of kerosene, equivalent to approximately 1 pint 

 to 6 square yards, was applied to each. The results, giving the number 

 of larvae alive at different periods of time after the commencement of 

 the experiment, are shown in tabular form. Of the larvae in the first 

 medium at the end of eight hours, only one was dead, while in the other 

 media only one was alive. At the end of 12 hours, the larva still alive 

 in the distilled water had died, while there was no change in the 

 condition of the other larvae, either then or at the end of 57 hours, 

 when the experiment was discontinued. 



The oil may be supposed to act in one of several ways, e.g., 

 by annulling the surface tension, by depriving the larvae of access to 

 the air, or by a poisonous action. The first hypothesis is not borne 

 out by facts, and the second is the theory which is most commonly 

 held. The poisonous action might take place in different ways : either 

 by the kerosene being dissolved in the water and acting on the larvae in 

 solution ; or by entering the tracheal tubes in the siphons when the 

 larvae come to the surface to breathe, and either blocking them or 

 spreading into the finer branches and acting directly on the tissues of 

 the larvae ; or again the vapour given off by the kerosene might act on 

 the larvae when it enters the tracheae during respiration. Obser- 

 vations made on larvae of S. fasciata showed that these may live for 

 several days under a film of kerosene, presumably obtaining the neces- 

 sary oxygen from the air bubbles; and those of Mansonioides 

 africanus, which do not require to come to the surface to breathe, 

 were apparently unaffected after three days and then pupated. 

 Experiments made to test the effect of kerosene vapour on 

 larvae showed that, when applied to those of S. fasciata and 

 Culex fatigans in a confined space, it causes them to become sluggish 

 and will eventually kill them. In the open however the vapour must 

 be very rapidly distributed by currents of air and probably is never 

 sufficiently concentrated long enough for its action to have any 

 importance. Larvae of C. fatigans in the fourth phase are almost 

 invariably killed within half an hour by oiling, but if they are prevented 

 from coming into actual contact with the film of oil, they survive longer. 

 Where larvae were confined under layers of kerosene and paraffin 

 respectively, but prevented from coming into actual contact with these 

 by plugs of cotton- wool, very little difference in the length of time that 

 the larvae survived in each case was observed, which shows that in this 

 case the action of kerosene was not specific, but only deprived the 

 larvae of access to air and so drowned them. Where a natural medium 

 was used, the larvae of C. fatigans survived for only about a quarter 

 as long as in distilled water, the organic matter present using up the 

 available oxygen and thus reducing the amount on which the larvae 

 could draw. In the case of S. fasciata larvae the action seemed to 

 differ on some occasions and the oil did not appear to have any direct 

 action on them. These larvae seem to be able to pierce the 

 film of kerosene with the valves of the siphon closed and may thus 

 avoid drawing the oil into the tracheae and so escape the direct action 

 of the kerosene, though if the oil does enter the siphon, it acts as a 

 direct poison as in the case of C. fatigans. In one experiment olive oil 



