NARCOTICS 321 



are used, the inhibition of photosynthesis is reversible. Kny (1897) 

 went to another extreme, and asserted that even plants which are almost 

 dead from chloroform poisoning continue to liberate oxygen; but his 

 experiments were sharply criticized by Ewart (1898). Kegel (1905) and 

 von Korosy (1914) made quantitative studies of the narcotization of 

 water plants, using the bubble counting method (c/. Vol. II, Chapter 25). 

 This work was analyzed by Schmucker (1928), who stressed the errors 

 to which bubble counting — which is never very reliable — can lead in the 

 presence of surface-active substances. Schmucker confirmed the re- 

 versibly inhibiting effect of low concentrations of chloroform and ether, 

 but attributed to an error the assertion of Kegel that high concentrations 

 of these narcotics may cause stimulation of photosynthesis. Schmucker's 

 own data (obtained mainly with Cabomha caroliniana) are given in 

 table 12. VII. Irving (1911), using excised cherry laurel and barley 



Table 12.VII 

 Effect of Narcotics on Cabomba caroliniana 



Chloroform: No stimulation by low concentrations. 



Reversible inhibition by 0.025-0.1% by vol. 



(0.0032-0.063 m./l.) 

 Injury and death by 0.1% by vol. 



Ether: Weak stimulation by 0.1% by vol. 



Reversible inhibition by 0.2-2.5% by vol. 

 (0.02-2.4 m./l.) 



Ethanol: Weak stimulation by 0.3-1% by vol. 



Reversible inhibition by 1-3% by vol. (0.17-0.52 m./l.) 



leaves, observed a much higher sensitivity to chloroform than that 

 found by Kegel and Schmucker with water plants. In her experiments, 

 0.001% by volume of chloroform vapor in the air stream was enough to 

 cause a complete stoppage of photosynthesis; a slightly larger concen- 

 tration made the injury irreversible. Wallace (1932), also working with 

 detached leaves (of Acer negundo), renewed the assertions of Schwartz 

 that chloroform and ether always cause an irreversible injury. 



Some observations on the effect of thymol on the photosynthesis of 

 Chlorella can be found in a paper by Emerson and Arnold (1932). 



Inhibition of photosynthesis by alkaloids (quinine, strychnine, mor- 

 phine) was observed by Marcacci (1895) and Treboux (1903). Accord- 

 ing to Treboux, complete inhibition is caused by 0.15% quinine chloride. 



Warburg, in 1919, introduced phenylurethan into the study of photo- 

 synthesis. From then on, compounds of this class became favorites in 

 all experiments on the narcotization of photosynthesis. The urethans 



O 



II 



are ethyl esters of alkyl carbamic acids: RNH — C — OCjHs. Their 



