CH. l] POISONS. 15 



In this experiment the CO2 acts, not by preventing 

 access of oxygen, but as a narcotic. This can be shown 

 by connecting with a hydrogen-generator, the rapid 

 retardation previously observed will be absent. 



(19) Ghloroform. 



The same apparatus serves to demonstrate the effect 

 of chloroform and other hurtful vapours. Shake up one 

 per cent, of chloroform in a bottle of water, through which 

 (by means of an aspirator) a current of air is made to 

 bubble. The air, thus charged with chloroform is allowed 

 to pass through the gas-chamber. The circulation can be 

 stopped without killing the leaf 



(20) Chloroform. 



The effects of poisons may also be conveniently demon- 

 strated on the leaf of Oooalis acetosella, using the colour 

 test already described. 



Shake up 1 c.c. chloroform in 200 c.c. water in a 

 stoppered bottle and add an Oxalis leaf cut into small 

 pieces. Note the time required for the discoloration to 

 occur. 



(21) Carbolic add. (Phenol.) 



Make the same experiment, substituting O'o per cent, 

 carbolic acid for chloroform-water. 



(22) Induced current. 



If an Oxalis leaf is impaled on a pair of needles (in 

 an insulated handle) connected with the induction coil, 

 the region between the punctures is killed and becomes 



