SCIENCE- G OS SIP. 



217 



■of dry bleaching powder is dissolved in a half- 

 pint tumblerful of water ; two ounces of washing- 

 soda are dissolved in another tumblerful of water ; 

 after which the two solutions are mixed together, 

 well shaken, and allowed to settle for twenty-four 

 hours or so. The clear fluid is then carefully 

 decanted, filtered, and preserved in a stoppered 

 bottle, away from the light. Sections or objects 

 to be bleached are first soaked in water, and then 

 transferred to a small quantity of the chlorinated 

 soda for a period of time varying from one to a 

 dozen hours or more. They must afterwards be 

 very thoroughly soaked or washed in several 

 changes of clean water until every trace of soda 

 is removed. 



The process of staining is as follows : Ten to 

 thirty drops of the stain, according to the require- 

 ments of the section or object, are added to an 

 ounce of distilled water, and the section is re- 

 moved from water to this stain, where it is allowed 

 to stand from ten minutes to half an hour, or even 

 longer. After washing in distilled water it is 

 generally recommended that the section be washed 

 in ordinary hard tap-water with a view to deepen- 

 ing the stain. We do not ourselves think this 

 necessary ; but if it is done, and if the tap-water 

 should not be sufficiently hard, about ten grains of 

 bicarbonate of soda added to a pint of distilled 

 water will serve the same purpose. The section 

 must then be promptly dehydrated by ten minutes' 

 or more soaking in methylated spirit, cleared in 

 clove oil until it sinks to the bottom, transferred to 

 turpentine, and mounted in Canada balsam. 



Overstaining with haematoxylin may be reme- 

 died by soaking a few minutes in a § per cent, 

 solution of glacial acetic acid in distilled water, or 

 in a solution made up of one part of 1 per cent, 

 hydrochloric acid in distilled water to two parts of 

 absolute alcohol. This also rectifies overstaining 

 with carmine. 



Eosin is likewise a useful stain, and may also be 

 used for double staining together with haemat- 

 oxylin. For double staining the section should be 

 stained with haematoxylin as above, then trans- 

 ferred to dilute acetic acid in distilled water. 

 After carefully washing away the acid, first with 

 distilled and then with tap water, stain for five 

 minutes or more in a 1 per cent, solution of eosin 

 in alcohol, wash well in methylated spirit, clear in 

 clove oil, and mount in Canada balsam. 



Borax carmine and acid aniline green are useful 

 for double staining vegetable sections. Mr. Cole's 

 method is frequently used and quoted, and is as 

 follows : The green stain is made up of two grains 

 of acid aniline green dissolved in a mixture of one 

 ounce of glycerine and three ounces of distilled 

 water. The carmine stain is made by dissolving- 

 ten grains of borax in one ounce of distilled water, 

 and adding half an ounce of glycerine and half an 

 ounce of absolute alcohol. Another solution is 

 then made of ten grains of carmine dissolved in 

 twenty minims of ammonia and thirty minims of 

 distilled water. The two solutions are then mixed 

 together and filtered. The process of staining is 

 to place the section in the green stain for five to 

 ten minutes ; wash in water ; place in the carmine 

 solution for ten to fifteen minutes ; wash well in 

 methylated spirit; dehydrate and clear in clove 

 oil ; wash in turpentine, and mount in Canada 

 balsam. 



The higher branches of section-cutting will be 

 beyond the necessities of the beginner ; but plant 



• sections of the simpler sort will be well within his 

 powers. Very fair sections can be cut with a razor 

 by holding the specimen between the finger and 

 thumb. The finger is held horizontally so as to 

 form a rest for the razor, the cut is made towards 

 the operator, and the razor is drawn through the 

 object with a diagonal drawing cut. A very simple 

 little hand microtome can be bought, however, for 

 five shillings and upwards. It contains a tube in 

 which the object to be cut is wedged between two 

 pieces of cork, pith, or carrot, or by imbedding in 

 paraffin. At the bottom of the tube is a fine screw 

 which raises the object as required after each cut, 

 and at the top of the tube is a circular flange of 

 brass or glass to serve as a guide for the razor. 

 The Cathcart microtome is, perhaps, the most 

 popular form, and is fitted with two parallel glass 

 runners, whilst the tube is provided with a clamp. 

 This is almost a necessity for paraffin imbedding, 

 as there is otherwise a tendency to slip in the tube. 

 The cheaper form, arranged for imbedding only, 

 would cost fifteen shillings. The short lengths of 

 tubes provided with the instrument as moulds for 

 paraffin blocks are, however, inconvenient. A much 

 better plan is to make little circular boxes of stout 

 paper or thin cardboard, or better still to use a 

 pair of brass L-shaped moulds, which are sold for 

 the purpose. It is as well to buy the paraffin, which 

 should have a melting-point of from 45° to 52° F., 

 according to the temperature of the room in which 

 it is to be used. If the paraffin is too soft the 

 sections will wrinkle, owing to lack of cohesion, 

 whilst if it is too hard they will roll up into tiny 

 rolls. The best way to proceed is to cut a small 

 slice of the specimen about a quarter of an inch 

 thick, dry it, melt the paraffin over a water-bath, 

 dip the section in the paraffiu to give it a coat, 

 hold it in the mould in the requisite position for 

 the desired cut, and run in the paraffin around and 

 over it, and allow to cool. As the paraffin will 

 shrink somewhat, especially at the top, the speci- 

 men should be well covered. When quite cool the 

 block can be removed from the mould and trimmed 

 to the shape necessary to go into the microtome 

 tube. With microtomes not fitted with a clamp 

 the tube itself must be used as the mould. The 

 razor used for cutting must be kept well sharpened, 

 and constantly wet by being dipped into a saucer 

 full of methylated spirit, the sections being floated 

 off as they are cut. The paraffin is then removed 

 by means of naphtha, benzole, or turpentine, the 

 turpentine washed off with alcohol, and the section 

 placed in absolute alcohol or water, as the case 

 may be. If it requires staining, this may be done 

 either on the cover-glass or the slide, the method 

 having been already explained. The subsequent 

 washing can be done with a small wash-bottle con- 

 taining water or 75 per cent, alcohol, as required. 

 Dehydrate with methylated spirit or alcohol of in- 

 creasing strength, clear with clove oil, and mount 

 in Canada balsam. Many sections are preferably 

 stained in bulk before imbedding. More com- 

 plicated processes, requiring special apparatus and 

 knowledge, such as infiltration or freezing, are 

 better left until skill and experience are gained in 

 the simpler processes. 



Spoilt slides, failures, etc.. are best immersed in 

 a strong, hot solution of Hudson's soap, after which 

 the slides and covers are well washed with warm 

 water, rinsed with methylated spirit, and polished 

 with an old handkerchief. 



(To be en a clmlcd.') 



