188 C. M. CHILD 



that the two factors, coefficient of distribution and rate of reac- 

 tion balance each other to some extent and that since the rate of 

 reaction has the greater temperature coefficient it determines the 

 result. Undoubtedly this is to a certain extent correct, but it is 

 difficult to understand how the relatively small temperature 

 coefficient of distribution can so nearly balance the much greater 

 temperature coefficient of rate of reaction. I am strongly inclined 

 to believe that another factor is involved here. The macerating 

 effect of benzamid is very great; the tissues seem almost to dissolve 

 in it. High concentrations of alcohol produce the same effect to 

 some extent and it appears to a greater extent in ether. It is 

 probable that disintegration in high concentrations of these and 

 many other substances which are highly fat-soluble is not solely 

 the result of the narcotic action, but in part of a change in physi- 

 cal condition in consequence of the solution of the substance in 

 the lipoids. The cells and tissues are undoubtedly dissolved to 

 some extent. This physical effect apparently hastens disintegra- 

 tion and often decreases the differences due to different rates of 

 reaction. With KCN this factor is eliminated for all practical 

 purposes, if it exists at all in that case. The concentrations of 

 KCN used are so very low that everything except the chemical 

 factor disappears from the result. For this reason results ob- 

 tained with substances which must be used in high concentration 

 or which are very highly fat-soluble should always be checked 

 by KCN. 



The concentration of benzamid used in Series 566, viz., 0.04 

 w., is more than double the minimal narcotic concentration for 

 either of the temperatures used. This concentration is near 

 saturation at 10°C., so that higher concentrations can be used 

 in temperature experiments only when higher temperatures 

 are used. But with higher concentrations the physical factor 

 undoubtedly becomes still more important, so that we should 

 expect the differences due to rate of reaction in the organism to 

 become less and less marked with increasing concentration. 



For comparison with Series 566 another series is given in which 

 the concentration used was lower, 0.02 m. ; this is only slightly 

 above the minimum. 



