HARDWICKE'S science-gossip. 



Ill 



but we will not answer for it. It would be possible, 

 we should imagine, for students to take several moulds 

 of a rare fish, and to exchange these with one an- 

 other, so as to get together a good collection of 

 British fishes. 



A WET METHOD OF PREPARING OBJECTS 

 FOR MICROSCOPICAL MOUNTING. 



IN the preparation of objects for permanent mount- 

 ing, the bite noir of the microscopist is the too 

 well-known and ever-recurring air-bubble. Books 

 on microscopy seem to recommend but one way of 

 mounting vegetable or animal tissues in the usual 

 preservatives, Canada balsam or dammar. And this 

 method is certainly, on the face of it, rather a peculiar 

 one. It is that of drying the object and then steep- 

 ing it for some time in turpentine. In fact, in order 

 to get rid of the small quantity of air contained in 

 some of the vessels, the whole of the object is filled 

 with air, and then this extra quantity of air (unne- 

 cessarily put in) has to be quietly soaked out again, 

 or is forcibly dragged out by the air-pump. This 

 process of filling up with air and then extracting it 

 again occupies no small amount of time, but, in some 

 cases, no such expenditure of misapplied patience, 

 even combined with the persuasions of the air-pump, 

 will entirely extract the air. 



Now, objects such as insects, sections of plants 

 and animals, may be prepared for mounting entirely 

 by a wet process, and that with speed and certainty. 



This wet method I have used for several years, 

 and I believed at one time that most of those inte- 

 rested in microscopical work must have known of it. 

 But of late, conversation with microscopical friends 

 has led me to imagine that it is little, if at all, known 

 to the mass of workers with the microscope. I 

 cannot suppose that the plan is original, though I 

 have not yet met with any one else that has worked 

 at it. 



The only piece of apparatus required is a single 

 test-tube. Into this the sections or parts of plants or 

 animals are placed, and the tube about half-filled 

 with distilled water that has been made acid with a 

 few drops of nitric acid. The liquid is now heated 

 almost to the boiling point for from five to fifteen 

 minutes. The acidulated water is then poured off, 

 and the tube filled with hot distilled water and gently 

 shaken once or twice. The water is now completely 

 poured off and replaced by methylated spirit ; this is 

 heated almost to its boiling point for about five 

 minutes. It is then poured off, and the tube about a 

 quarter filled with ether, and the contents heated 

 gently by immersing the end of the tube in a cup of 

 hot water for half a minute. Ether, being highly 

 inflammable, should not be heated by, nor brought near 

 to, a light. Now pour off the ether and quickly drop 



in a quantity of turpentine that will a little more than 

 cover the objects. The whole operation is now 

 finished, and every particle of air and water originally 

 in the object has been replaced by turpentine. The 

 objects are now ready for mounting in Canada balsam 

 or dammar. 



There need be no waste of materials, since the 

 methylated spirit and the ether may each be poured 

 into separate residue bottles, and, after a quantity has 

 been collected, be re-distilled without any loss worth 

 mentioning. 



In this method we first fill the object with its 

 natural permeator, water, and then replace this with 

 methylated spirit. This latter, being of greater 

 tenuity, enters into some of the minuter vessels which 

 the water has still left only filled with air. 



Ether is next made to take the place of the spirit, 

 and this, from its marvellous tenuity, rapidly fills any 

 vessels that the spirit even had perchance failed to 

 fill. Thus a road, as it were, having been made 

 for fluids, turpentine easily and rapidly spreads 

 throughout the object. I know that there is a 

 process somewhat similar in which oil of cloves is 

 used. But oil of cloves has not the same extreme 

 tenuity as ether, and so does not permeate tissues 

 anything like so thoroughly as ether does. It is also- 

 rather expensive, and does not readily admit of being 

 used over and over again. 



The advantages of the wet process are its economy 

 of materials, its leaving the object almost unaltered 

 in appearance, its cleanliness, and, above all, its 

 extreme rapidity and certainty. 



Only a single test-tube is required in which a dozen 

 or two of objects may be placed at one time. 



The re-agents, with the exception of the water and 

 acid, which are not worth saving, may be used again 

 and again. 



In drying an object, since all the water which made 

 up so much of its bulk is driven off, its shape is often 

 greatly altered, its original form being only partially 

 restored by the after processes. By the wet method, 

 the cells are never empty of liquid ; of course, both 

 spirits and ether shrink objects to some extent, but 

 the turpentine and balsam usually all but entirely 

 restore the original form. As to the time taken, the 

 drying method often requires weeks ; the wet method 

 seldom needs an hour. There are some objects 

 which I have never seen entirely freed from air by the 

 drying process, followed by prolonged soaking in 

 turpentine and the use of the air-pump ; but I have 

 not yet seen an object that the wet process would not 

 rapidly free from air. It is possible by this method 

 to cut three or four fresh sections from a tree, per- 

 manently mount them in Canada balsam or dammar 

 without a single bubble of air, ring them with coloured 

 cement, and label them within the hour. 



The use of nitric acid is not a necessity, but it 

 quickens the process. Sometimes it is better to use 

 in its stead a little potash, only then the objects 



