EXPERIMENT STATION BULLETINS. 583 



at once, in the dark. The glow then, when once started, seemed to 

 depend upon some oxidition process. 



Now, in the dark room, if a wet paper supporting one of the glow- 

 ing- photogenic organs was introduced into a test tube containing vapor 

 of carbon disulphide, the light would rapid]}' dim and the organ become 

 invisible. If removed at once to pure air, the glow would reappear gradu- 

 ally, but it never became quite as bright as before. 



Carbon disulphide therefore, in the presence of air, could produce the 

 same result as pure carbon dioxide — i. e., as the absence of oxygen. 



This effect of carbon disulphide upon the luminous organs of P. 

 pennsylvanica, taken in connection with its effect upon the respiratory 

 quotient of insects furnishes additional evidence that this insecticide 



(as also the others which produce similar effects upon the ^^^ ) is 



able to interfere directly with the taking up of oxygen by the insect- 

 tissues. 



The question naturalh- arises — can it be that the mere presence, 

 alone, of the vapors of carbon disulphide, kerosene, gasoline, turpen- 

 tine, and similar volatile oils tend to prevent something, in the tissues 

 from uniting with oxygen to start the oxidition process. Such a thing^ 

 seems not impossible, when it is remembered how a very slight per 

 cent of many of those same vapors will check or prevent moist phos- 

 phorus from taking up oxygen. 



II. SOME PROPERTIES OF LIME-SULPHUR WASH THAT MAKE 



IT EFFECTIVE IN KILLING SCALE. INSECTS— 



ESPECIALLY SAN JOSE SCALE. 



Lime-sulphur is discussed, here, somewhat apart from the other in- 

 secticides. The reason for this will be apparent in the following pages. 



When this insecticide was tried upon large insects, having rather 

 heavy chitinous walls, it seemed to have very little effect. Specimens of 

 Passaliis cornutus and large tomato-worms were not killed even after 

 being submerged for two minutes in lime-sulphur solution of the 

 strength recommended as a winter spray. They showed some irritation 

 for a time but this wore off in most cases with no apparent permanent 

 injur}'. Upon more delicate insects with thin chitin, the irritation was 

 greater, apparently, and if the wash were applied to a small portion of 

 a very delicate body- wall (like the body of a covered scale insect) that 

 part might be killed before the rest of the body. But no means couW 

 be found to prove, satisfactorily, that the lime-sulphur wash had pene- 

 trated into the body. 



Now lime-sulphur is recognized as a special rather than as a general 

 contact insecticide. It has been recommended by entomologists as an effec- 

 tive agent against scale insects (particularly San Jose scale) more, 

 perhaps, than against any other form of insect life. San Jose scale is 

 found living in a partially grown condition under its small scale-cover- 

 ing at a time of year (Fall, Winter, Spring) when the wash can be 

 applied strongest without injury to the tree. 



