56 



SCIENCE 



[N. S. Vol. XXXI. No. 785 



the probable impermeability of the cell 

 membranes to this highly toxic salt in the 

 case of the resistant forms. I am inclined 

 to believe myself, however, that it is prob- 

 ably not so mnch due to such causes as 

 to specific differences in the constitution 

 of the protoplasm itself, which renders the 

 usually poisonous substances relatively in- 

 operative. There hardly seems enough evi- 

 dence to support the idea of any very highly 

 specialized qualitative selective power on 

 the part of the cell membranes in the mat- . 

 ter of dissociable and diffusible salts. On 

 the other hand, there are many reasons for 

 looking upon protoplasm not as a uniform 

 substance, but as differing considerably in 

 different plants. The fact that some plants 

 can not thrive except in the complete ab- 

 sence of oxygen is enough to illustrate this 

 point. The condition of the stimulated 

 plant may itself cause a variation in the 

 optimum concentration of the stimulant, as 

 is shown by the effect of rise in tempera- 

 ture on the lowering of the toxic or stimu- 

 latory dose. It is not only among lowly 

 organized plants like fungi that stimula- 

 tion follows such conditions, but among the 

 higher vascular plants as well. We can not 

 suppose that these stimulants react directly 

 upon the protoplasm or themselves supply 

 the energy necessary for the changes which 

 they induce with a possible reservation in 

 the cases of those salts whose valency may 

 be subject to change. In the first place, 

 they fall in very different groups of toxic 

 substances, if we take Loew's well-known 

 classification, and yet there is a great simi- 

 larity in the reaction produced. Therefore 

 it is reasonable, for the time being, to dis- 

 regard to a considerable extent the ques- 

 tion of the chemical nature of the stimu- 

 lating substance as far as its effects in ac- 

 celerating the life processes of the organ- 

 ism are concerned. This does not mean, 

 however, that the ultimate effect on the 



manner in which these poisonous substances 

 may, in strong solutions, kill the proto- 

 plasm is not related to the chemical nature 

 of the toxic agent. Not only are the stim- 

 ulants not the sources of energy for the 

 changes involved, but also they can not, in 

 most cases at least, be regarded in them- 

 selves as catalyzers, no matter how greatly 

 the end result of their action might suggest 

 their being of such a nature. If, therefore, 

 we are to find any satisfactory clue to the 

 answer to the question of the influence of 

 these minute doses, we must look rather 

 towards the indirect effect they may exert 

 and endeavor to discover if they may not 

 encourage the formation by the protoplasm 

 itself of substances which do act in a cata- 

 lytic fashion. It seems clear, then, that the 

 poisonous action of a given substance may 

 be, and probably commonly is, very differ- 

 ent from the stimulating effect of small 

 doses of the same substance. 



Whether it is safe to say that all sub- 

 stances which are toxic must of necessity 

 act as stimulants if presented in suffi- 

 ciently dilute form is a question. It is con- 

 ceivable that some might produce no reac- 

 tion unless present in a lethal dose, but it 

 seems probable that most substances will 

 show a stimulating reaction at the proper 

 dilution. In this connection it is well to 

 remember that we should not confuse the 

 necessarily more complicated reaction of 

 higher animal forms, whose balance of 

 function is so delicate and whose tissue 

 structures are so very diverse, with the 

 more fundamental and presumably simpler 

 and more direct reactions of the less inter- 

 dependent cell aggregations such as are 

 found in plants. It is reasonable to sup- 

 pose, however, that as far as the cells them- 

 selves are concerned the underlying prin- 

 ciples are much the same in all organisms. 



Upon inquiring more closely into the 

 effects of stimulants, we find that while a 



