112 Odier on the Chemical composition 



stitutes one of the elements of the hydrocyanic (Prussic) acid, and 

 according to Dr. Thomson, probably enters also into the compo- 

 sition of Indigo ; and Mr. Brande has very lately proved its exist- 

 ence in the vegetable salifiable bases, Cinchonia, Quinia, Mor- 

 phia and Strychnia.* Some animal substances, on the contrary, 

 are not found to contain any nitrogen, as picromel, and the animal 

 oils, including fat. The discovery of M. Odier, if it be one, is 

 not therefore absolutely new in a chemical sense, though none of 

 the substances enumerated above have any analogous functions in 

 the animal or vegetable economy, nor any external resemblance to 

 his Chitine, which he, not unaptly, considers to bear that relation 

 to insects, &c. that the woody fibre bears to plants, and which, 

 according to him, it most nearly resembles in its most obvious 

 properties. 



M. Odier is led to his conclusion that Chitine contains no 

 nitrogen, from the phenomena, amongst others, which it pre- 

 sents when burnt in contact with the air, and especially from 

 its not giving off any carbonate of ammonia when distilled in close 

 vessels. I shall not dispute the accuracy of either of the facts, 

 but it seemed to mc, on reading his Memoir, that the absence of 

 nitrogen requires to be proved in a less equivocal manner than by 

 the mere negative result, that the volatile products of its distilla- 

 tion have no effect on the test papers exposed to their influence, 

 before we can safely adopt his conclusion that the Chitine is 

 really destitute of that element. Suppose an acid, the acetous for 

 instance, to be simultaneously formed in the distillation ; ammonia 

 might be evolved and yet escape detection by the test applied. 

 Such a case is at least possible, and the experiments I am about to 

 relate, render it, I think, not very improbable that it may have 

 occurred in the present instance. 



The season of the year (winter) in which I made my experi- 

 ments, precluding the possibility of obtaining a sufficient quantity 

 of the same insects as those Odier operated on, I selected, because 

 most easily procured, the common Cantharides of the shops — Lytta 

 Tesicatoria, Linn. — Cantharis versicatoria of Olivier and Latreille. 



* Journal of Science, vol. 16, p. 279. 



