1 873.] INSECTIVOROUS PLANTS. 323 



the physiology of the plant soon led him into regions 

 where his knowledge was defective, and here the advice and 

 assistance which he received from Dr. Burdon Sanderson was 

 of much value :] 



C. Darwin to J. Burdon Sanderson. 



Down, July 25, 1873. 



My dear Dr. Sanderson, — I should like to tell you a 

 little about my recent work with Drosera, to show that I 

 have profited by your suggestions, and to ask a question or 

 two. 



1. It is really beautiful how quickly and well Drosera and 

 Dionaea dissolve little cubes of albumen and gelatine. I kept 

 the same sized cubes on wet moss for comparison. When 

 you were here I forgot that I had tried gelatine, but albumen 

 is far better for watching its dissolution and absorption. 

 Frankland has told me how to test in a rough way for 

 pepsine ; and in the autumn he will discover what acid the 

 digestive 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. 



Y 2 



