N 



Chap. VIII.] CONCLUDING REMARKS, ACIDS. 161 



tive process of animals. Formic acid induces very slight in- 

 flection, and is not poisonous; whereas, its ally, acetic acid, 

 acts rapidly and powerfully, and is poisonous. Malic acid 

 acts slightly, whereas citric and tartaric acids produce no 

 effect. Lactic acid is poisonous, and. is remarkable from in- 

 ducing inflection only after a considerable interval of time. 

 Nothing surprised me more than that a solution of benzoic 

 acid, so weak as to be hardly acidulous to the taste, should 

 act with great rapidity and be highly poisonous; for I am 

 informed that it produces no marked effect on the animal 

 economy. It may be seen, by looking down the list at the 

 head of this discussion, that most of the acids are poisonous, 

 often highly so. Diluted acids are known to induce n^ative 

 osmose,* and the poisonous action of so many acids on 

 Drosera is, perhaps, connected with this power, for we have 

 seen that the fluid in which they were immersed often became 

 pink, and the glands pale-coloured or white. Many of the 

 poisqnous acids, such as hydriodic, benzoic, hippuric, and 

 carbolic (but I neglected to record all the cases), caused the 

 secretion of an extraordinary amount of mucus, so that long 

 ropes of this matter hung from the leaves when they were 

 lifted out of the solutions. Other acids, such as hydro- 

 chloric and malic, have no such tendency; in these two 

 latter cases the surrounding fluid was not coloured pink, and 

 the leaves were not poisoned. On the other hand, propionic 

 acid, which is poisonous, does not cause much mucus to be 

 secreted, yet the surrounding fluid became slightly pink. 

 Lastly, as in the case of saline solutions, leaves, after being 

 immersed in certain acids, were soon acted on by phosphate 

 of ammonia ; on the other hand, they were not thus affected 

 after immersion in certain other acids. To this subject, 

 however, I shall have to recur. 



* Miller's ' Elements of Chemistry,' part 1. 1867, p. 87. 



