Livingston : Chemical stimulation of a green alga 33 



Nature of toxicity 



Although a number of attempts have been made to find out 

 what it is in the nature of these toxic substances which mves them 

 their stimulating power, there has been practically no outcome of 

 it all until the appearance of Mathew's paper above referred to. 

 Practically all of the toxicity series which have been made out 

 seem to agree in certain respects, r. ^., they do not follow the 

 valence of the elements involved, nor do they follow the order of 

 atomic weights ; on the other hand, it is usually evident that, in 

 some sort of a general way, they do depend upon the chemical 

 nature of these elements, the more inert atoms always appearing 

 as of low stimulating power while Cu, Ag, Pt, etc., lie at the op- 

 posite end of the series. This much is as evident from my work 

 as it is from that of Kahlenberg and True, Clark and Mathews. 



The last-named author has discovered a remarkable similarity 

 between his toxicity series and three chemical serfes formed on the 

 basis, respectively, o{ solution tension^ atoniic volume^ and ^function 

 obtained by dividing the equivalent xvciglit by the atomic volume^ 



m 



With none of these series my results agree accurately, but a com- 

 parison of his published tables with those here presented (page 2q) 

 will show some remarkable points of resemblance. It would ap- 

 pe.ar from a comparison of all the work available on this subject 

 that, Avhile the suggestion of the author just named seems to fall 

 short of explaining the relation of toxicity in general to chemical 

 properties, yet he has at least given us the only rational basis for 

 exploration of this difficult field. 



That different organisms behave differently in the same solu- 

 tion is to be expected from the mere fact that they are different 

 organisms,/. ^., that their protoplasms are not identical. The 

 points of similarity in different protoplasms have become so strongly 

 emphasized (as is illustrated by the fact that we use the single 

 term protoplasm to include them all), that their essential points 

 of difference have often been partially lost sight of. The toxicity 

 series for any form is doubtless conditioned by a complex function 

 derived, on the one hand, from the properties of its protoplasm as 

 an organic mixture and a colloidal solution, and, on the other^ 

 from some such properties of the elements as those considered by 



Mathews. 



