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Note on the Excrements of certain Insects. By John Davt, 

 M.D., F.R.S., Lond. & Edin., Inspector- General of Army 

 Hospitals. Communicated by the Author. 



For some years it has been known that the urinary excre- 

 ment of the silk-worm consists chiefly of lithic acid. I am not 

 aware that the inquiry has been extended further, or that the 

 excrements of any insects have been examined ; — if they have, 

 I have met with no account of the experiments. 



Favourable opportunities often occurring in Barbadoes for 

 prosecuting the research, I have occasionally availed myself of 

 them ; and I shall now briefly notice some of the results which 

 I have obtained. 



Grass-hopper. — There are two species common in this island 

 — one brown, the other green ; both larger than the grass- 

 hopper of our English fields. The excrement from them is in 

 small cylindrical masses ; some almost black, others of a fawn 

 colour; the former faecal, the latter urinary. The latter, 

 heated with nitric acid, efl'ervesces and acquires the rich 

 purple colour characteristic of lithic acid ; and under the mi- 

 croscope is seen to consist chiefly of minute granules. 



Beetle. — A black beetle, about the size of the Scarabceus 

 pilularius, is common here, and, at one season of the year, 

 abundant and troublesome at night, owing to the strength and 

 wildness of its flight, striking against objects in the most heed- 

 less manner. A single one confined in a wine glass, voided on 

 the third or fourth day of its confinement a large quantity 

 (in proportion to the bulk of the beetle) of very light fawn- 

 coloured matter, almost white, soiling not only the bottom of 

 the glass, but a good part of the insect itself. Under the mi- 

 croscope it was found to consist of globules from g oVo to s o^o o 

 of an inch in diameter, without crystals or any other form of 

 matter. Tested by nitric acid, it proved to be lithic acid, ac- 

 quiring, when duly heated, the peculiar rich purple colour, 

 which it instantly imparted to water. 



Wasp. — The wasp of this island is very similar to the Eng- 

 lish wasp, but larger, and probably a diff^erent species. A 

 breeding-comb, with a small colony of this insect, was confined 



