163] 



THE GOLDFISH AS A TEST ANIMAL— POWERS 



43 



Minutes 

 1680 



1560 



1440 



1320 



1200 



1080 



960 



840 



720 



600 



480 



360 



240 



120 



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 23. Superimposition of survival time curves of the alkali and alkaline earth metals 

 as chlorides showing crossing over of curves, thus showing varj-ing relative to.xicities of the 

 group when different definite survival periods are taken as a criterion. 



to the utilization of the death point as a criterion and points out the fact that 

 "it is impossible to determine the precise moment of death." He has shown 

 that the death curve "approaches the axis asymptotically." He suggests 

 that it may be assumed that as the reaction proceeds certain phenomena 

 appear at definite points on the curve. He took as his criterion a point on 

 the curve at which he said that the organism was "half dead." The writer 

 has found the same objections pointed out by Osterhout but has come to the 

 conclusion that the death point with certain precautions is a more exact cri- 

 terion for an end point in the case of the goldfish than the loss of equilibrium 

 or irritability. Aside from the objections raised by Osterhout there is a still 

 more serious objection to any attempt to determine relative toxicities by 

 comparing the concentrations of the solutions or the amount of the substance 

 necessary to produce death or the appearance of any physiological phenom- 

 enon in any arbitrary fixed time or the concentration necessary to just cause 



