Cuar. VIIL] CONCLUDING REMARKS, ACIDS. 161 
and many other acids of the same strength, and is not 
poisonous. This is an interesting fact, as hydrochloric acid 
plays so important a part in the digestive process of animals. 
Formic acid induces very slight inflection, and is not poison- 
ous; 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 inducing 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 negative 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 poisonous 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 hydrochloric and malic, 
have no such tendency; in these two latter cases the sur- 
rounding 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 cer- 
tain 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 i. 1867, p. 87. 
