NOVEMBEE 1, 1912] 



SCIENCE 



575 



It should be borne in mind that a concen- 

 tration far too weak to affect one organism 

 injuriously may be toxic for another. Con- 

 centrations of sodium chloride which are 

 too low to affect certain flowering plants 

 may be quite toxic to certain algae and 

 mce versa. 



The study of such relations, especially 

 in the case of organic soil substances, is 

 now being carried forward. 



2. Stimulatory Action. — ^A considerable 

 number of toxic substances (including 

 such salts as sodium chloride) exert at 

 certain concentrations a stimulating effect 

 on metabolism. It is quite possible that 

 this belongs to the same category as the 

 catalytic action of enzymes and of mineral 

 salts. It also seems quite probable that 

 the stimulating substances often play the 

 role of kinases. How this may come about 

 is illustrated by the germination of the 

 castor bean. In this ease it is necessary 

 that the fat stored in the seed be split up 

 by the action of an enzyme (lipase) but 

 this can not act rapidly except in the pres- 

 ence of an acid (kinase). The role of the 

 acid appears to be to cause the enzyme to 

 swell and emulsify. The castor bean pro- 

 duces suificient acid for this purpose, but 

 it is clear that in other cases the kinase 

 may be absorbed from without and may 

 sometimes be furnished by another organ- 

 ism. There is reason to suppose that kin- 

 ases include a great variety of substances, 

 both organic and inorganic. 



It is quite possible that stimulating sub- 

 stances may act in other ways, as, for 

 example, by altering the permeability of 

 the protoplasm. 



3. Nutrient Action. — As was said in the 

 beginning, we are not yet sure in all eases 

 what nutrient substances are needed nor 

 what their role is in the plant. To take 

 but a single example we may select cal- 

 cium. So important is it that we find 

 plants classified ecologically into those 



which prefer lime soils and those which 

 avoid them. A high authority very graph- 

 ically describes how in the Mississippi 

 Valley, in passing a region rich in lime to 

 one where it is less abundant, the appear- 

 ance of the trees changes: from being 

 densely branched with thick foliage they 

 become sparsely branched, so much so that 

 the former region is avoided by squirrel 

 hunters because the game can too easily 

 hide in the dense tree tops. The crops 

 become less and less, while barns and 

 houses grow smaller as the soil grows 

 poorer in lime. 



Various hypotheses have been advanced 

 to explain the effects of calcium. It was 

 supposed to play an essential part in pho- 

 tosynthesis, but it appears that some of the 

 lower green algffi may carry on photosyn- 

 thesis in complete absence of calcium. 



It was also supposed to form (in com- 

 bination with proteid) an indispensable 

 part of the nucleus, but many fungi and 

 some of the algse thrive without it, despite 

 the fact that their nuclei and mitotic proc- 

 esses are apparently similar to those of 

 plants which require calcium. 



A more satisfactory view of this ques- 

 tion is possible from the standpoint of 

 protective action. 



4. Protective Action. — It is well known 

 that many toxic effects may be overcome 

 more or less completely by the addition of 

 other substances. When one substance 

 thus acts as an antidote to another it is 

 said to have a protective action. It is by 

 no means necessary that the protective sub- 

 stance should itself be toxic, though it fre- 

 quently is so; nor is it necessary that it 

 should have any nutritive value. A large 

 number of cases are now known in which 

 mineral salts act as more or less efficient 

 antidotes to other salts or to organic sub- 

 stances. 



If we apply these principles to the case 

 we have just now discussed, namely, the 



