122 



HARD WICKE ' S S CIE NCE- G O SSI P. 



the turpentine or other clearing agent, that they 

 become mere mummified caricatures of the originally 

 plump structure. Animals provided with a chitinous 

 armour suffer, of course, much less in this way ; but 

 even with them the shrinking action is very percep- 

 tible, and I can see no advantage whatever in resinous 

 over glycerine mounting. Moreover, when the cell is 

 of any depth, the intrusion of bubbles during the 

 prolonged process of drying is a source of continual 

 annoyance. On this account I am accustomed to 

 use glycerine or glycerine jelly for all forms save 

 shelled mollusca and worms. For the former 

 glycerine is undesirable, on account of its action on 

 their shells ; for the latter, because for some reason 

 neither this nor any other medium that I have 

 tried preserves them in anything like their pristine 

 beauty. 



A strong solution of chloride of calcium, to which 

 has been added a little glycerole of salicylic, or boracic 

 acid, proved more satisfactory than anything else 

 experimented with ; but a good preservative is a 

 great desideratum, as when first taken such things as 

 Polynae, etc., are amongst the most beautiful of our 

 captures. For mollusks nothing is better than mount- 

 ing in spirit ; but in this hot climate such mounts 

 lack permanence, so that chloride of calcium is 

 usually used for them also. 



A good supply of cells, of all possible depths — 

 from a mere ring of cement to glass rings \ in. deep — 

 is indispensable to the microscopist who wishes to 

 preserve his captures permanently. The material of 

 these is a matter of little moment, but for all' except 

 the deepest, where glass or vulcanite is preferable, I 

 have come to prefer metal rings cemented with marine 

 glue. Two points are important : first, to make use 

 of cells no deeper than is absolutely necessary ; 

 second, to employ thin glass slips, in order that it 

 may be possible to examine both sides of the objects 

 under moderate powers. For cases where it happens 

 to be specially desirable to be able to examine both 

 sides, it is a good plan to have ready a number of 

 cells, to one side of which a thin cover has already 

 been cemented. By wetting the outer surface of this, 

 it will adhere to an ordinary glass slide quite firmly 

 enough to hold it while the process of mounting is 

 completed in tbe usual way. When the cement has 

 dried, the little box is placed in the opening in one 

 of "Carpenter's" wooden slides, and retained in 

 place by a couple of perforated labels. For this 

 purpose broad-edged vulcanite cells are the best, as 

 their large outer dimensions permit of the cement 

 being inspected, and fresh coatings, if necessary, 

 applied without disturbing the paper labels. 



Before quitting the subject of mechanical tech- 

 nique, let me describe a method of obtaining thin 

 sections of Fntomostraca and other minute crusta- 

 ceans, which is, I believe, somewhat novel. On 

 account of their small size and the hardness of their 

 chitinous coats, they do not lend themselves well to 



the paraffin method, as the knife is apt either to ride 

 over them or to compress them, and drive out the 

 paraffin filling up their interstices. Moreover, on ac- 

 count of the bulk of the apparatus and the difficulty 

 of maintaining a constant temperature by means of 

 spirit-lamps, it is extremely difficult in practice to 

 carry it out on shipboard. The method to be de- 

 scribed is, however, a somewhat rough and uncertain 

 one, and it is only occasionally that results at all 

 comparable to those of the paraffin method are ob- 

 tained. It is, moreover, applicable only to very 

 minute organisms. The course of procedure is as 

 follows : The animal is taken from absolute alcohol 

 and immersed in oil of cloves, where it is left until it 

 is completely clarified. It is then placed in a watch- 

 glass containing a few drops of Canada balsam (un- 

 diluted), and placed over a spirit-lamp at such a 

 height as to melt without danger of burning the 

 balsam. In about a quarter of an hour the balsam 

 has driven out the clarifying agent, and penetrated 

 throughout the entire structure of the animal. A 

 single drop of balsam is now placed on a glass slip, 

 and heated until it cools hard. Now take up the 

 animal, together with a bead of balsam, on the point 

 of a needle, and place it on the balsam on the slide, 

 previously warmed, and prop it up in such a position 

 that the plane of the sections desired may be parallel 

 to that of the slide, holding it thus until the balsam 

 has cooled sufficiently to keep it so. 



There is just one consistency of balsam at which 

 it may be readily sliced with a razor, without stick- 

 ing to the blade, and yet is not brittle ; and it is 

 this condition which it is desired to obtain for the 

 bead on the slide. Accordingly, when quite cold, it 

 should be tested with the edge of a scalpel. If too 

 soft, the slide must be warmed over the lamp for a 

 while ; if too hard, it must be removed from the 

 slide and replaced in the watch-glass, to which a 

 drop of fresh balsam has been added. In the! diffi- 

 cult}' of obtaining exactly the right consistence lies 

 the uncertainty of the method ; but, when this is hit 

 upon successfully, really beautiful sections can be 

 most easily obtained by slicing down the bead with a 

 sharp razor or lancet, as in the ordinary hand method. 

 The sections may be allowed to fall from the razor 

 on to the slide until all the material is exhausted, 

 and then covered with dilute balsam, under a large 

 cover-glass, or they may be picked up one by one on 

 the point of a needle, and arranged in order on a 

 separate slide, which has been varnished with a thin 

 coat of balsam so as to retain them in their respective 

 places while mounting. The method is also useful 

 for obtaining sections of coralline Algre, whose struc- 

 ture, when deprived of their lime, is so rotten that 

 it is extremely difficult to mount even the smallest 

 sections whole, unless supported by some exception- 

 ally linn imbedding material. 



I have little more to add. The present papers are 

 intended to be but a description of methods and 



