498 CLIMBING AND INSECTIVOROUS PLANTS. [1S74. 



C. Darwin to F. C. Donders.* 



Down, July 7, 1874. 



My dear Professor Donders, — My son George writes 

 to me that he has seen you, and that you have been very 

 kind to him, for which I return to you my cordial thanks. 

 He tells me on your authority, of a fact which interests me 

 in the highest degree, and which I much wish to be allowed 

 to quote. It relates to the action of one millionth of a grain 

 of atropine on the eye. Now will you be so kind, whenever 

 you can find a little leisure, to tell me whether you yourself 

 have observed this fact, or believe it on good authority. I 

 also wish to know what proportion by weight the atropine 

 bore to the water solution, and how much of the solution was 

 applied to the eye. The reason why I am so anxious on 

 this head is that it gives some support to certain facts repeat- 

 edly observed by me with respect to the action of phosphate 

 of ammonia on Drosera. The ^wcTo fo of a g ram absorbed 

 by a gland clearly makes the tentacle which bears this gland 

 become inflected ; and I am fully convinced that ■gTnr o 1 oooo of 

 a grain of the crystallised salt (i.e. containing about one-third 

 of its weight of water of crystallisation) does the same. Now 

 I am quite unhappy at the thought of having to publish such 

 a statement. It will be of great value to me to be able to 

 give any analogous facts in support. The case of Drosera is 

 all the more interesting as the absorption of the salt or any 

 other stimulant applied to the gland causes it to transmit a 

 motor influence to the base of the tentacle which bears the 

 gland. 



Pray forgive me for troubling you, and do not trouble 

 yourself to answer this until your health is fully re-estab- 

 lished. 



Pray believe me, 



Yours very sincerely, 



Charles Darwin. 



* Professor Donders, the well-known physiologist of Utrecht. 



