1904.] of Acids and Bases in respect of Paramcecium aurelia. 103 



Table II. 



Hiiilin, whose ionic concentration (4- 3 x 10~ 6 N) is about one five- 

 hundredth of that of lithium hydrate (1960 x 10~ 6 N) for a nearly 

 equal lethal effect. 



The metallic alkalies can be arranged in two periodic groups, the 

 mean lethal concentration of .the one (K, Na, Li) being greater than 

 that of the other (Ca, Sr, Ba), when Paramoecia are killed in nearly 

 equal times. Further, the lethal effect runs parallel to the periodic 

 order of these .metals, as is exhibited in Table III, in which the atomic 



Table III. 



weights are given, and the lethal periods repeated from Table II. 

 When the hydrates of calcium, strontium and barium are employed in 

 solutions of weaker concentration, so as to permit of a more accurate 

 determination of the lethal period than is possible when observation 

 extends over so short a period as 5 minutes, it can be shown that 

 strontium hydrate is less toxic than barium hydrate, but the difference 

 between the latter hydrates is much less than that between strontium 

 and calcium hydrates. Similarly the difference in lethal character 

 between sodium and potassium hydrates is much less marked than that 

 between sodium and lithium hydrates. It is not possible, owing to 



