EFFECT OF ANAESTHETICS 6l 



be twenty seconds ; application of feeble stimulus enhanced 

 this rate by 17 per cent. The intensity of stimulus was now 

 gradually increased in the manner already described. This 

 caused a diminution of the rate by 20 per cent. ; a slightly 

 stronger stimulus induced a greater retardation of the rate 

 by 35 per cent. Further increase of stimulus brought about 

 a total arrest of evolution of oxygen. After moderate 

 stimulation, the normal rate was found to be gradually 

 restored in the course of about half an hour. Excessive 

 stimulus, however, caused death and permanent abolition 

 of photosynthesis. 



Effect of Anaesthetics 



In the study of the effect of anaesthetics and other 

 chemical agents on photosynthesis it is necessary to ob- 

 serve first the normal rate of evolution of oxygen, and then 

 the change in the rate after the introduction of the chemical 

 agent into the plant-vessel. This must be done without 

 causing any mechanical disturbance to the plant, since 

 mechanical or electrical irritation modifies the normal rate 

 of photosynthesis. A special plant-vessel had therefore 

 to be devised for quick introduction or withdrawal of the 

 normal C0 2 -solution, and of the C0 2 -solution with a certain 

 percentage of the chemical agent added to it. The plant- 

 vessel is shown in fig. 14. A hollow stopper h with a hole o 

 is fixed on a stand l. The lower end of the plant-vessel 

 with a T-tube is fitted exactly to the stopper. When the 

 vessel is rotated through 90 , the hole o comes opposite 

 to the T-tube, and the liquid is withdrawn from the vessel. 

 A funnel-tube f is then exactly fitted to the T-tube : the 

 solution containing the chemical is poured through the 

 funnel, taking care that the level of the liquid inside the 

 plant-vessel always comes up to the mark m. The vessel 

 is afterwards rotated through 90 °, when communication 

 with the funnel-tube f is cut off, and the funnel-tube 

 is then removed. 



