135] 



THE GOLDFISH AS A TEST ANIMAL— POWERS 



15 



time curve from that of an equilateral hyperbola. To summarize: in the 

 lithium chloride and all toxic substances tested with the exception of CuCl2, 

 CdCl2, and to a certain extent FeCla the following conditions were met: — 



1. A concentration (the point C, about 0.073 N. Li CI), the threshold of 

 toxicity concentration, was found below which the goldfish were not killed. 



2. Just above the threshold of toxicity concentration the rate of fatality, as 

 expressed by the reciprocal of the survival time, increased very slowly with 

 increase in concentration of the toxic substance employed. This is represented 

 by the portion C to A, about 0.073 to 0.19 N. LiCl, of the velocity of fataUty 

 curve CABG (Fig. 1). 3. With higher concentrations, concentrations 



0.05. 0.1. 0.15. 0.2. 0.25. 0.3. 0.35. 0.4 0.45. 0.5. 0.55. 0.6N. 



Figure 4. Ammonium chloride 



sufficient to kill the goldfish in not less than 54 to 58 minutes and not more 

 than 234 to 310 minutes in hthium chloride solutions, the velocity of fatality 

 increased more rapidly in proportion to the increase in concentration of the 

 toxic substance, and this portion of the velocity of fatahty curve approaches 

 a straight line. (The portion A to B, curve CABG, Fig. 1.) Table XXIV 

 shows minimum and maximum survival time of goldfish and concentration 

 of toxic substances tested where its velocity of fatality curve approaches a 

 straight line. The daggers (f) in Tables I to XXIII also indicate the con- 

 centrations of the substances and the survival time of the goldfish where 

 their velocity of fatality curves approach a straight line. 4. At stUl higher 

 concentrations (0.375 to 0.45 N. LiCl) the increase in the velocity of fatality 

 was again less rapid in proportion to the increase in concentration of the 



