32 Dr. John Davy's Observations, Sic. 



The proportional quantity of the urinary secretion of birds, and 

 the large quantity of litliate of ammonia which exists in it, — is 

 indeed its principal part,* — is remarkable ; — we have proof of it, 

 whether we examine the excrement of any single bird, or direct 

 our attention to the immense beds of guano, of which the urine 

 of birds, variously changed, appears to be the chief ingredient. 

 Nor is the urine of insects in relation to quantity less remark- 

 able. In examining it, I have often been surprised at its abund- 

 ance. In my notes, when mentioning the excrement of the moth, 

 No. 16, which weighed little more than a grain and a half, I find 

 the remark, that its excrement exceeded in quantity — it was 

 similar in kind — that of a humming-bird which I was examining 

 at the time, and which weighed 92*5 grains. The musquitoe, 

 and its urinary secretion, may be adduced as another illustration, 

 as well as of the delicacy of the test employed to detect the 

 organic acid. In your letter to me, that already referred to, 

 adverting to the importance of insects in the economy of nature, 

 after noticing their number, how probably 250,000 species may 

 be estimated to exist, you specially point to one function of this 

 great class, — the eating of plants and the converting them into 

 animal matter fit for the food of birds, fishes, &-c. Another part, 

 in harmony with this, may be pointed out, viz. how by their 

 excrement, especially the urinary portion of it, they contribute to 

 manure and fertilize the earth for the production of plants, on 

 which so many of them depend for a subsistence. We have seen 

 in the examples last given — the four last — that the peculiar uri- 

 nary secretion may be detected in the dead insect, after many 

 months, in accordance with the character of lithate of ammonia. 

 This quality of endurance, I need hardly remark, fits it admirably 

 for a persistant manure. 



I am. 



My dear Sir, 



Yours very truly, 



John Davy. 

 Lesketh How, Ambleside, 

 Dec. 17, 1853. 



* Without any exception, I believe the urinous secretion of birds is princi- 

 pally lithale of ammonia. I have found it such in every instance that I have 

 examined it, whatever the kind of food; in the instance of the graminivorous 

 birds, such as the goose and the swan, the lithate incrusts the fajcal excrement 

 commonly much in the same manner as I have found it incrusting the same 

 excrement from beetles. 



