220 moderator: s. hestrin 



dormant ones by this method, and also heat-shocked spores 

 from dormant spores. By refining the density differences, one 

 should be able to separate spores with varying degrees of 

 dormancy. 



Moderator: As a bystander one has the impression that 

 microbiologists are fully aware of this aspect of the problem and 

 that they are directing adequate efforts to the working up of 

 reliable assay procedures. This may not be equally true, how- 

 ever, in relation to some of the more compHcated biological 

 systems. Would you like to comment. Dr. Lees, on good quanti- 

 tative techniques for work with insects. 



Lees: The selection of the most suitable and the most stand- 

 ardized material for insect dormancy studies has not really been 

 a problem. You choose your insect according to your purpose ; 

 for endocrine system studies you choose a large insect, like a 

 giant silkmoth. For studies on, say, photoperiod, a quickly 

 multiplying species is preferable. Unfortunately, such an insect 

 is usually an inconveniently small subject for surgery. Lepidop- 

 tera of moderate size have nevertheless been used rather exten- 

 sively for both purposes. The silkworm of commerce, with its 

 different genetic races, has been a particularly favoured species. 



Moderator: Might it not be useful to concentrate within a 

 given insect on one particularly suitable tissue? 



Lees: If you mean a tissue suitable both for biochemical work 

 and for the study of cell structure during dormancy, the epider- 

 mis should prove to be a good choice. It forms a fiat layer only 

 one cell thick and is easily stained and preserved as a whole 

 mount. Wigglesworth has shown that when moulting is induced 

 by injection of ecdyson, detectable cytological and cytochemical 

 changes occur within 24 h. Shappirio has also used wing epithe- 

 lium for in yivo spectroscopic studies. 



Moderator: Could one cut this tissue up and put it in a test 

 tube? 



Lees : The epidermis could certainly be separated and studied 

 biochemically. But if you are referring to the possibiUty of 

 tissue culture, the prospects are not bright. As for organ culture, 



