22 Applied BiopJiysics 



terns. Owing to the high resistance of the cuticle, drugs may 

 be appHed to the insect at concentrations which would be rapidly 

 toxic to less resistant organisms. When an aqueous solution 

 (10%) of ethyl alcohol is injected into the blood of the blowfly 

 larva, Calliphora crythroccphala, the insect is rapidly paralyzed, 

 but will remain active in pure alcohol for more than an hour 

 when this is applied externally. It is clear that the alcohol 

 cannot penetrate through the cuticle into the tissues of the 

 insect. If the alcohol is now diluted (1:1) with a fat solvent, 

 such as kerosene, whicli is by itself nontoxic, the insect is killed 

 in less than a minute, starts to swell owing to the rapid penetra- 

 tion of alcohol into the tissues, and bursts explosively in about 

 4 minutes, during which time the body weight has increased by 

 some 50% (figure la). If the insect is transferred from the 

 alcohol-kerosene mixture to pure alcohol when the body weight 



'$. 50 



V. 40 



<u 

 u. 

 o 



C 30 



bo 



C 



(U 



u 

 u 



20 



10 



/i 4- 



if- 



I .' 



F 



•«■= 1 1 1 1 \ \ 1 1 I 



10 



Period of immersion (minutes) 



FIG. 1. Uptake of Ethyl Alcohol by Blowfly Larvae (Calliphora 



crythroccphala). 

 a Continuous immersion in alcohol -|- kerosene mixture. 

 b Alternate immersion in alcohol + kerosene mixture and pure alcohol. 

 X Bursting point of insects. 



= alcohol + kerosene. 



=■ alcohol. 



