496 CLIMBING AND INSECTIVOROUS PLANTS. [1873. 



sin ; and in the autumn he will discover what acid the digest- 

 ive juice contains. 



2. A decoction of cabbage-leaves and green peas causes 

 as much inflection as an infusion of raw meat ; a decoction 

 of grass is less powerful. Though I hear that the chemists 

 try to precipitate all albumen from the extract of belladonna, 

 I think they must fail, as the extract causes inflection, whereas 

 a new lot of atropine, as well as the valerianate [of atropine], 

 produce no effect. 



3. I have been trying a good many experiments with 

 heated water. . . . Should you not call the following case 

 one of heat rigor ? Two leaves were heated to 130 , and had 

 every tentacle closely inflected ; one was taken out and placed 

 in cold water, and it re-expanded ; the other was heated to 

 145 , and had not the least power of re-expansion. Is not 

 this latter case heat rigor? If you can inform me, I should 

 very much like to hear at what temperature cold-blooded and 

 invertebrate animals are killed. 



4. I must tell you my final result, of which I am sure, [as 

 to] the sensitiveness of Drosera. I made a solution of one 

 part of phosphate of ammonia by weight to 218,750 of water; 

 of this solution I gave so much that a leaf got 8 ^ 00 of a grain 

 of the phosphate. I then counted the glands, and each could 

 have got only tttJffo °f a grain ; this being absorbed by the 

 glands, sufficed to cause the tentacles bearing these glands to 

 bend through an angle of 180 . Such sensitiveness requires 

 hot weather, and carefully selected young yet mature leaves. 

 It strikes me as a wonderful fact. I must add that I took 

 every precaution, by trying numerous leaves at the same time 

 in the solution and in the same water which was used for 

 making the solution. 



5. If you can persuade your friend to try the effects of 

 carbonate of ammonia on the aggregation of the white blood 

 corpuscles, I should very much like to hear the result. 



I hope this letter will not have wearied you. 



Believe me, yours very sincerely, 



Charles Darwin. 



