fly around in the vicinity of a person or in fact land also represent a certain irritation the number of biting mosquitoes is the decisive factor for the period of effectiveness and thus in the tropics for the risk of infection isopropyl myristate represents an additive which ensures that application of the insect repelling agent produces a pleasant sensation on the skin the three aforesaid formulations were applied to the skin as described above and the test already described was performed the period of effectiveness was assumed to have ended when at least two mosquitoes bit and sucked blood in the treated area during a test period fig1 shows the test results for the three formulations i e the formulation without glycerol formulation with 10 glycerol and formulation with 40 glycerol the period of effectiveness in hours is plotted on the ordinate it is evident from this that even with a concentration of only about 10 glycerol the period of effectiveness is increased to 11 hours as compared to a formulation without glycerol 5 hours with a formulation containing 40 glycerol it was possible to increase the period of effectiveness to 13 hours in a further test series an insect repelling agent with the peg 400 adjuvant was compared to a formulation according to.