CHANGES IN ENVIRONMENT OP DAPHNIA MAGNA. 205 



This curve is represented in the accompanying diagram 

 (Fig. 1). Between the limits of 0'9 per cent, and GO per 

 cent, solutions the curve is well represented by a rectangular 

 hyperbola, and we have the relation T(.t— 8) = constant, 

 where T = the time of killing, and x = the strength of salt 

 solution between the limits of the 9th and GOth units. 



The relation may be shown in a tabular form thus : 



'J^BLE II. 



Mean of the products T (a; - 8) = 276-6. 



Thus in no case do the products T(a; — 8) diverge very 

 widely from the mean 277. To show how rigorous is this 

 test it may be remarked that one minute error in the 

 observation, say at 3 per cent, solution, would make a 

 difference of 22 in the product. 



According to these experiments solutions below "9 per cent. 

 and above G'O per cent, appear to introduce different sets of 

 causes from those between these limits. 



Perhaps there is something more than mere analogy with 

 Boyle's Law, which states that, with certain restrictions 

 and between certain limits, PV is constant for any gas where 

 P = pressure and V = volume, the temperature being fixed. 

 Volume may be compared with the amount of salt in the 

 solution above a certain ' ?;ero ' percentnge [-8 per cent.). 



