40 JOURNAL OF THE [April, 



been used continuously ever since in our laboratories. Its- 

 decided neutral reaction or indifference toward most chemical 

 reagents renders this a unique material for a cell-wall, from a 

 chemical point of view. It is but slightly soluble in alcohol, 

 though freely in ether, benzol, xylol, and turpentine. It is. 

 miscible with fixed or volatile oils when melted, and, I believe, 

 slowly when cold. Fortunately its strong solvents are rarely or 

 never employed in the constitution of preservatives. 



The fitness of paraffin for cell-making has repeatedly occurred 

 to microscopists at home and abroad. A few years ago a sug- 

 gestion of its use for cells was published in a German scientific- 

 journal ; and more recently it has been recommended by F. N. 

 Pease' simply for ringing balsam mounts. 



Nevertheless its use appears still to be limited, if not unknown, 

 in many laboratories, and no reference is made to it in the last 

 edition, by Dallmger, of Carpenter's work on "The Microscope."" 

 This has been caused, I think, by its insufficient adherence to glass. 

 Early in its use we 'found this defect indicated,fat times, by the 

 inability of a liquid mount in a paraffin cell to bear moderate 

 pressure without easy rupture, generally at the bottom of the 

 cell, next the slide. Paraffin, in cooling, does not form a homo- 

 geneous solid, but a congeries of crystals, often comparatively 

 coarse. Its deficiency seemed to call for the addition of some 

 substance of greater adhesive power, whose diffused particles 

 would also serve as nuclei to induce the consolidation of the 

 paraffin in a more minutely crystallized mass. This was easily 

 accomplished by previously saturating the parafifin with one of 

 the strongest cements, balsam-cement ; the result has proved 

 entirely satisfactory after use for nearly ten years. The follow- 

 ing are the details of the simple method. A supply of balsam- 

 cement is first prepared by slow evaporation of commercial 

 Canada balsam, in a shallow tin pan, over a low flame, until the 

 point is reached of wax-like consistence on cooling, as tested on- 

 drops removed and cooled from time to time. 



For the parafifin the hardest variety in commerce is used, with 

 highest melting point, above 45° C (113° F.). After the stock 

 of this (say one-quarter of a pound) has been heated over a low 



' Micr. Bull., vii. C1890), i. 



