526 



Journal of Agricultural Research 



Vol. XIII, No. II 



PENETRATION OF LIQUIDS INTO THE TRACHEAE 



From the results of Cooper and Nuttall (2) it would appear necessary 

 to make a determination of the surface tension of the insecticide, the 

 surface tension of the chitin, and the surface tension at the interface of 

 the chitin and the insecticide before it could be determined whether or 

 not the liquid would spread over the body and penetrate the tracheae. 

 From the results of Bigelow and Hunter (j), however, the capillary rise 

 in a tube really determines whether the adhesion between the liquid and 

 the solid is greater than the cohesion of the liquid, or, in other words, is a 



Fig. I.— Sketch of a trachea of the cockroach divided into sections A, B, C, etc., to indicate the distance 

 the various oils penetrated. See Table I. 



means of determining whether the surface tension of the solid is greater 

 than the surface tension at the interface between the solid and the liquid 

 plus the surface tension of the liquid. By placing an insect in the insec- 

 ticide to be studied for a short period and then dissecting it, it is possible 

 to determine whether or not the insecticide has penetrated the tracheae, 

 and approximately how far. These results give an index of the spreading 

 ability of the different materials. 



The cockroach (Blatella germanica L.) was used in the following experi- 

 ments for determining the penetration of insecticides into the tracheae. 

 The results were checked over with certain of the compounds using the 

 wax-moth larvae (Galleria mellonella) , the larvae of the Indian meal moth 



