612 THE MICROSCOPE, 



differ from him. I have never seen in this membrane, 

 when completely separated from the calcareous matter, 

 any trace of this nacreous lustre, and consequently believe 

 it to be due entirely to the carbonate of lime, and not to 

 the membrane on which it is deposited. In my experiments 

 I have always employed the polariscope, which furnishes 

 the best means of deciding this point. Moreover, the 

 nacreous lustre of a piece of shell is not in the least im- 

 paired by boiling it for any length of time in liquor potassce, 

 and but little so by heating it to redness, which must have 

 been the case if the lustre were produced by the delicate 

 folds of what Dr. Carpenter has called the nacre-mem- 

 brane." 



P. 236.] My friend Mr. Millar writes me first with 

 regard to the siliceous structure of wheat, &c. : 



" A few years ago, whilst examining the siliceous skele- 

 ton of the grasses with the Rev. J. B. Reade, I discovered 

 that, by adding carefully to the hot nitric acid and 

 vegetable matter some strong sulphuric acid, almost im- 

 mediate solution took place of the vegetable matter ; and 

 in this way the process, instead of requiring hours for its 

 accomplishment, was completed in a few minutes. 



"ON MOUNTING INSECTS. 



" In mounting whole insects, or parts of insects, I first 

 soak them in the ordinary liquor potasses of the Pharma- 

 copoeia, for a period varying with the density of the chitine 

 and the amount of muscular fibre to be softened. They 

 are then to be washed in water, and pressed until the 

 muscular tissue is got rid of. The object may then be set 

 out with water in the position it is intended to remain in, 

 on a slide ; cover it with another, tie them together, and 

 then immerse in turpentine ; in a few hours, the turpen- 

 tine hardens the chitine, and, if allowed to remain long 

 enough in it, will displace all the water. The object is 

 then to be mounted in balsam in the usual way ; should 

 any water still remain in the object, it will cause a milki- 

 ness to appear around it when the cover is pressed down. 

 The cover must be removed and the object washed in 

 turpentine, as long as any milkiness is seen. If the legs 



