133] 



THE GOLDFISH AS A TEST ANIMAL— POWERS 



13 



TABLE IV 

 Potassium Chloride. Temperature 20.5° C. November 17, 1916 



dra^vn resembles that of an hyperbola and has been designated as the survival 

 time curve the nature of which can be better illustrated by drawing the re- 

 ciprocal curve. In the reciprocal curve the reciprocal of the survival time of 

 the goldfish is plotted as ordinate. The normality is plotted as in the survival 

 time curve. To avoid the use of fractions 100 over the survival time is taken as 

 the reciprocal. One block ordinate represents one unit reciprocal. The circles 

 f •) represent the location of the reciprocals. The curve CABG is drawn by in- 

 terpolation and has been designated as the velocity of fatahty curve. By an ex- 

 amination of this curve it is seen that it rises very slov/ly from the point C to A, 

 i.e., in low concentrations, more rapidly from A to B, i.e., in higher concentra- 

 tions, and again there is a falling off from B to G at still higher concentrations. 

 By a closer examination of the curve it is seen that the portion from A to B 

 approaches a straight line and for all practical purposes this portion can be 

 considered as such. The point C where this curve cuts the X-axis has been 

 designated as the actual threshold of toxicity concentration, i.e., the concen- 

 tration below which the substance ^\dll not kill the goldfish. The portion 

 of the curve from A to B is not a straight line but approaches a straight line 

 in that the direction of curvature is being reversed from that of the curvature 

 from C to A to that of the curvature from B to G (See velocity of fatahty curves, 

 Figures 1 to 21.) For a further discussion of the velocity of fatality curve 

 see pages 48, 52. The portion from A to B of the curve CABG if considered as a 

 straight line and prolonged cuts the X-axis at the point P. The curve PABF 

 thus drawn has been designated as the theoretical velocity of fatahty curve 

 and the point P has been designated as the theoretical threshold of toxicity 



