ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1101 



the lamp for a short time, the slides were put on a warm kitchen 

 mantel-jiiece for two or three hours, and on examining them a week 

 afterwards they were found to be quite free from moisture. 



Mr. E. Ward thinks * that if the moisture could get out of a paper 

 cell it could also get in, unless it is sealed up at precisely the right 

 moment with protective cement, and the difficulty is as to when is the 

 right moment. He prefers to use a metal cell, to be careful to have 

 dry objects, and having got rid of the moisture from the gum, &c., to 

 seal up the cell. In this way he has mounted thousands, few of which 

 have shown even a trace of moisture or fungi. 



His plan is this. Having mounted an object in the cell and 

 allowed it to become thoroughly dry, spin a ring of bro'mi cement 

 upon the cell and let it dry till it can be indented with the iinger-nail 

 without sticking. Then warm a cover-glass, and place it on the cell. 

 Choosing then a strong glass slip, make it hot in the centre by means 

 of a spirit-lamp, and press it down on the top of the cover-glass ; 

 the warmth melts the cement, and the cover is fixed firmly without 

 evaporation inside the cells. 



The slide should now be put away for a day or two for the cement 

 to harden, and then, if another layer is applied, we may be sure of a 

 dry mount. 



White Zinc Cement-t— Dr. F. L. James briefly recapitulates the 

 objections which have been made to this cement, and his answers 

 thereto. 



It is objected (1) that it does not attach itself firmly and evenly 

 to glass at all points ; (2) that it is brittle when dry, and easily cracks 

 and scales oif ; (3) that it is peculiarly liable to " run in " under the 

 cover-glass ; and (4) that it is unreliable. 



To these he replies: — (1) That if the cement works well at one 

 time it certainly will do so at any and every other time, if the same 

 conditions exist. A cement that attaches itself to glass at one point 

 will do so at all points, if the surface is equally ready to receive it ; 

 but if one part of the surface is clean and dry, and another is dirty 

 or moist, or both, no cement can be expected to act upon it with 

 uniformity. (2; A cement made as hereafter described will neither 

 scale nor crack, as a proof of which he can exhibit mounts made with 

 it twelve or thirteen years ago, and which have been carried many 

 thousands of miles with no especial precautions against breakage, and 

 which are yet perfect. (3) As to the liability of the cement to run 

 when used with balsam mounts, the fact is admitted ; but it will do 

 so only when the proper precautions against such an accident have 

 been neglected. (4) " It is the very height of folly and absurdity to 

 charge an inanimate substance with caprice and unreliability. If it acts 

 well at one time and fails to do so at another, the fault lies not with 

 the substance, but with its manipulator." 



White zinc cement made as follows, has. Dr. James considers, no 

 superior for general microscopical purposes : — Dissolve gum damar 

 in pure benzol sufficient to make a s(dution of the consistency of 



* TraiiH. an<l Ann. Ilcp. MancJi^Htcr Micr. Sof., 1884-.'), pp. .33-0. 

 t St, Louis Nufional Druggibt, vii. (1885) p. 181. 



