INTRODUCTION. XXXV 



The mode of fixing the insect in Canada balsam 

 is very simple : a slip of glass is warmed over a 

 candle, and a drop of the balsam is then placed upon 

 it ; the insect, whilst yet alive, is placed on the bal- 

 sam, and the glass is then again very gently warmed, 

 in order to kill the insect ; another piece of the glass 

 is then heated over a candle, and placed on the in- 

 sect, when the creature will be hermetically sealed 

 up for ever. It is necessary that the insect should be 

 dry when it is mounted, and we must take especial 

 care not to apply too much heat, which will corrugate 

 the antennae, and destroy the form of the insect. 



The strips of thick, and pieces of thin glass, I 

 always procured of Mr. Topping, No. 1, Penton- 

 place, Pentonville-hill, who is moderate in his charges 

 and exceedingly obliging. 



I strongly recommend to all entomologists this 

 mode of preserving small insects, and having once 

 properly secured them, they will last for an indefi- 

 nite period, and can be handled without the slightest 

 risk of injury. 



It is admitted on all hands that the disease in the 

 potatoe plant itself is a local or general death. Now 

 the death of a plant may arise from ten thousand 

 causes, independently of the present cause, which is 

 effecting the total destruction of the potatoe plant 

 Under these circumstances, in conducting our inves- 

 tigations, we must isolate solitary causes of death 

 and confine our attention to the particular agent which 

 so universally affects the potatoe plant. A plant may 



