STRUCTURE AND ACTIVITY 



459 



3 4 5 6 



Number of carbon atoms 



Figure 8. Distribution functions and toxicity in the aliphatic primary alcohols. 

 Curve 1, solubility (pM per liter); curve 2, equitoxic concentration (jiM per liter) 

 for Eberthella typhosa; curve 3, concentration (p.M per liter) reducing the surface 

 tension of water to 50 dynes per centimeter; curve 4, vapor pressure at 25° 

 (mm x 10 4 ); curve 5, partition coefficient (x 10 3 ) between water and cottonseed oil. 

 Redrawn from Ferguson (104), by permission of the Cambridge University Press. 



critical distribution or site of action. Nor do studies of this type offer 

 the hope of determining the actual site of the toxic action. 



It is true, however, that at present the distribution function most 

 susceptible of experimental attack is permeability. That is, changes 

 in toxicity coincident upon changes in thermodynamic activity must be 

 investigated first to see whether the answer lies in the greater rate of 

 entrance of the less water-soluble compounds into the cell. In the 

 aliphatic alcohols, permeability is almost certainly not the answer: 

 toxicity increases rapidly as the molecular weight increases, but all mem- 

 bers of the series penetrate very rapidly, and differences in rate of en- 

 trance do not explain differences in toxicity (79). 



Toxicity does not, of course, increase indefinitely in a homologous 

 series. Above a certain chain length, the exact point depending on the 

 series and on the test organism, toxicity falls off sharply. This cutoff 

 is a reflection, probably, of insolubility of and micelle formation by the 

 higher members of the series (18, 53, 417). 



The non-specific poisons are often referred to as "physical" toxicants, 





