338 Dr Davy's Additional Notice on the 



urinary secretion, from the experiments which I have made 

 on it, appears to be another distinctive mark compared with 

 that of the different species of insects which I have hitherto 

 examined. In the secretion from the spider, I have not been 

 able to detect any lithic acid, but what I believe to be the 

 zanthic oxide. Whether obtained from a spinning or from a 

 hunting spider, the character of the matter voided in con- 

 finement has been similar ; abundant as to quantity ; semi- 

 fluid at first, soon becoming solid ; of the lustre of wax ; most 

 readily diffusible in water, to which it imparts a milky hue ; 

 neither acid nor alkaline as tried by test-papers ; and under 

 the microscope appearing to be composed of very minute 

 granules, varying in size from 20000 ^^ 30000 i^ch in dia- 

 meter. It was found soluble, and that readily, in the nitric, 

 sulphuric, and muriatic acids, and also in the acetic and ox- 

 alic. It did not impart colour to either of these acids when 

 the solution was made without the aid of heat ; but with heat, 

 in the instance of the nitric acid, a compound of a lemon-yel- 

 low colour was obtained ; and in that of the sulphuric, a 

 slight yellow tinge was produced. I have found it also solu- 

 ble in aqua potassa, and in a solution of the sesquicarbon- 

 ate of this alkali, but not in aqxia ammoniee, nor in a solu- 

 tion of the bicarbonate of potash. Heated on a platinum foil, 

 it bore a pretty high temperature without apparent change ; 

 more strongly heated, it consumed without flame, leaving a 

 very minute quantity of matter, which, exposed to nearly a 

 white heat, melted, and exhibited under the microscope 

 minute globules. Subjected to a decomposing temperature 

 in a glass tube, it yielded pretty much water and carbonate 

 of ammonia, and some carbonaceous matter. 



The properties I have described, as found to belong to this 

 excrementitious matter, are those of the zanthic oxide ; and, 

 consequently, it may be considered as composed chiefly of 

 this oxide. 



I have examined the excrement of, at least, three different 

 species of spider, and of several individuals of the same spe- 

 cies, and I have found it in its qualities and composition re- 

 markably uniform. Sometimes its colour has been a little 

 grayer than at others, which I believe to be owing to a 



