54 ILLINOIS BIOLOGICAL MONOGRAPHS [174 



DISCUSSION OF DATA 



All substances investigated show very striking similarities in their toxic 

 activities on the goldfish. 1. All substances show a slow relative increase in 

 rate of velocity of fatality with increase of substance used when time required 

 for fatality is above 720 minutes. 2. The greatest rate of increase of velocity 

 of fatality occiu^s when amounts of substances used wiU kill the goldfish in 

 periods from about 45 minutes to about 210 minutes vA\h only a few exceptions. 

 (Table XXIV). 3. The rate of increase of velocity of fatality is less rapid 

 with increase in concentration of the substance used when the time required 

 to kill the goldfish is less than about 45 minutes. 4. When the velocity of 

 fataUty is plotted as ordinate and normality or the amount of substance used 

 per Uter as abscissa, the curve thus formed has a very striking resemblance 

 to a monomolecular autocatal)^c curve, i.e., it is a logarithmic curve. HCl 

 and KCN show this character more strikingly than other substances tested 

 as experiments were run over a large range of concentrations. (Figures 14 and 

 15.) 5. The velocity of fatality of the goldfish is more nearly constant for 

 any given concentration when the concentration of toxic substances used is 

 sufficient to kiU the goldfish in a period of not less than 45 minutes nor more than 

 210 minutes, with very few exceptions. The range for KCN and HCl is 

 from about 90 minutes to about 1800 minutes. This range must be determined 

 independently for each substance. (Table XXTV.) 6. The velocity of 

 fataUty curve approaches a straight line for amounts of substances that will 

 kiU the goldfish in periods of time just mentioned. This range must be deter- 

 mined independently for each substance by the graphic method from experi- 

 mental data. (Table XXTV and Figure 1 and explanatory notes.) 



From these general results it is seen that when the toxic value or active 

 principle of any substance is to be determined from a pharmacodynamic assay 

 point of view; i.e., to determine the strength of an unknown, only such portions 

 as wiU kill the goldfish within a range of a certain minimum and maximum time 

 should be used. This range must have been previously determined for each 

 substance to be tested. (See 5 and 6 above and Table XXTV^.) An unkno^vMi 

 can be determined by any one of five methods. 1. A definite survival time 

 can be utilized, ^.e., determine the concentration of the substance that ^^•ill 

 kill the goldfish in a selected period of time. The survival time of the goldfish 

 for most exact determinations should be within the range of time where the 

 velocity of fatahty curve approaches a straight line. This range of time must 

 have been previously determined for each substance to be tested. The portion 

 A to B of the velocity of fataUty curve, (Fig. 1 and Table XXTV^.) This is a 

 modification of the method proposed by Pittenger and Vanderkleed (1915). 2. 

 A number of goldfish can be killed in the unknown and the average survival 

 time taken and appUed directly as ordinate to a survival time curve of the same 



