598 



12. RATES OF INHIBITION 



Examples of Concentration-Time Relationships 



The lethal action of Cu++ on Nitella is expressed fairly well by the equa- 

 tion (Cu'*"'")"^ = C, where n is about 0.33, and the plots of log t against 

 log (Cu+"^) are straight lines to the first approximation (Cook, 1926 c). 

 The killing of paramecia by arsenite, however, requires the equation 

 [(I) - (I),J"^ = C, where (!),„ = 1 mM, n = 1.38. and C = 1.21 M min 

 (Neuschlosz, 1919), these value being obtained from the linear log-log 



Fig. 12-40. Logarithmic plots of the concen- 

 tration-time curves in Fig. 12-39 (Eq. 12-91). 



plot (Fig. 12-42). It may be noticed that actually the experimental points 

 could be connected somewhat better by a curve concave downwards, so 

 that the above equation is only an approximate expression of the kinetics. 

 Comparison between different members of a series of compounds can also 

 be made on such graphs. The killing of trypanosomes by various arsenicals 

 provided kinetics that gave quite linear log-log plots (Hawking, 1938) 

 as shown in Fig. 12-43. The constants calculated are shown in the following 

 tabulation. 



