JiLY. 1902.] 



KNOWLEDGE, 



165 



Conducted by M. I.Chpss 



PoXD-Liri; Collect! Nti in .Iri.v. — CoUectins,' in July is 

 usually not so profits! ble as one would expect, because as a rule 

 most of the shallow ponds are dried up by this time, or have been 

 reduced to a muddy swamp, and in the others the Crustaceans, 

 Cladocera and Cyclops, have multiplied to such an extent as to 

 leave little room for the more interesting forms of pond-life. 

 This year, however, is likely to prove an exception to the rule, 

 the weather all through the spring having been quite two 

 months behind its usual season. 



Pedtilion miruiii should be looked for in largo and small lakes, 

 as it will probably have greatly increased in numbers. The 

 somewhat rare and very large Asplanchna umphnra and ebhealidnii, 

 as well as Asjthmhtinpux mi/nneleo. are summer forms which 

 occur at this season. Other Rotifers that appear in warm 

 weather are : Ihnnps longipes, Tri/Jii/lltis Idcitxtrh, Xntop.i 

 (■l(i)-ulalii<. Si-aiittiiiin I'tnlartiloliiin, and I'inii/rtfidtiiu, then the 

 free-swimming f.ariniiliir/n milntis and Cunurhilus rolrnx, also 

 the fixed J.driniilnrhi soc/nlin and Meiinlntrorlia, which are found 

 attached to submerged water plants. All these are very beautiful 

 objects under the microscope, but by no means common. 



Vithoj- i/loluitor will certainly be found in abundance now in 

 secluded ponds, and inside the green spheres the little parasitic 

 Kotifer, Proitlex jHirasilira, should be looked for. 



The Polyzoa, mentioned last month, will have become more 

 abundant where they occur ; undisturbed ornamental lakes and 

 canals .are the best places to find them in. 



Hints on Section Cutting. — Success in microtome section 

 cutting, no matter what microtome be used, ciin only be properly 

 attained by dexterity in free-hand section cutting. A few 

 directions which will indicate the manner in which this desir- 

 able facility may be secured may, therefore, be of value. Itciills 

 for patience, care, and considerable practice. 



It will be well to select some botanical subjects of small 

 diameter and not too hard in substance to experiment upon, 

 bearing in mind that the smaller the diameter of the material 

 the easier will it he to cut good sections. 



The material should be placed in a bottle of i'O per cent. 

 alcohol for three or four days before cutting, and when the 

 operation is in |)rogress, a cup .'hould be provided to receive the 

 razor also containing '.HI per cent, alcohol, a saucer with the 

 same spirit in it to dip the material in. and another to receive 

 the sections. A sable-hair brush will also be required of the 

 size known as crow-quill ; camel-hair bru.shes being useless. 



The material should be held verticiilly between the thumb 

 and index finger of the left hand, allowing it to n^st in the first 

 bend of the finger and keeping the thuml) | inch below the level 

 of the finger. The upper end of the material to be cut should 

 be about level with the finger, the razor being held lightly but 

 firmly, chiefly with the thumb and index finger of the right 

 hand. Wall wet the material and razor with the alcohol, place 

 the blade of the razor flat upon the inde.x finger of the left 

 hand and cut the thinnest possible transverse section by either 

 drawing the razor towards you diagonally through the material 

 and cutting from heel to point, or bj- pushing the razor away 

 from you and cutting from point to heel. As each section is 

 cut, it should be lightly brushed from the razor into the saucer 

 of alcohol, and when, say, one hundred sections have been made, 

 the thinnest and best half dozen may be selected and the process 

 repeated for jinictice. A further .seleclioii of the best may then 

 be made. 



It may now be well to say a few words on the implements 

 that are ueces.«ary. 



The Il.\/.()i:.^Three ])atteriis will be found useful for trans- 

 verse section cutting, as figured A, B,and C. A, being suitable 

 for large objects, or those harder than the average ; B, for 



ABC 



rTT 



general use ; and C, for small and delicate objects. Quality 

 of steel and sectional shape go hand in hand with form 

 of blade. The edge should be 

 A B C fairly str.iight and tlie heel 



rounded, not angular ; the 

 handle should be one that is 

 capable of being grasped pro- 

 perly. Heavy uncouth razors 

 must be avoided : so also 

 should one having any letter- 

 ing engraved on its blade. 

 The blade should be as broad 

 as possible, J" being a good 

 width. The razor must bo kept free from corrosion, and the 

 edge ranintained always at its keenest by careful attention 

 immediately after use. 



To set a razor.— The time will quickly come when the edge 

 of the razor will become notched, and in order to restore the 

 edge a hone must be used, a strop being useless for the purpose. 

 The Hone. — A very good hone, known as "water of Ayr 

 stone,'' may be obtained for about J.s. The size of its 

 sharpening surface should bo 9 in. bv "i in. Water, not oil, should 

 be used as the lubricant, and it will be found to be a good ])lan 

 to allow a stream of water to flow continuously over the hone 

 during the whole time of sharpening. 



Care should be taken not to scratch the hone. Scalpels, 

 needles, or any other such small instruments should never be 

 allowed to visit it. Having the hone flooded with water, la}' 

 the razor flat and diagonally upon the left of the hone in such 

 a manner that the edge of th(^ razor is towards the right, and 

 entirely upon the hone. Draw the razor lightly but firmly edge 

 forwards, and from heel to point along the hone to the extreme 

 right. Turn the razor with a neat action of the fingers combined 

 with a turn of the wrist, its back being kept on the hone, and 

 draw the edge forwards from heel to point as before, from right 

 to left. 



Maintain this process to and fro until the notch is removed, 

 remembering always that the lightest pressure will secure the 

 best and quickest results. In fact it is impossible to hone a 

 razor by hard pressure. When the notch is removed by honing, 

 the edge of a razor when carefully examined with a lens x 10 

 diameters should present throughout its length a straight line, 

 with perhaps here and there a slight fringe or jaggedness 

 standing out from the straight edge, the so-called wire edge. 

 This may be removed by stropping. 



The razors, with one side flat, must only be honed upon the 

 concave side, and are more difiicult for the novice to sharpen 

 than the other forms. Having dried the razor and returned 

 the hone to its place, we now finish the sharpening by means of 

 the strop. 



The Strot. — Many kinds of strops may be purchased from 

 the dealer. To a new hand the shilling cushion strop will be 

 quite good enough to practise on, subsequently a better strop 

 maj' be obtained, and the first, although probably damaged by 

 cuts, will be useful for sharpening scalpels. Opinions ditter as 

 to the best form of strop, but we have a person.-d fancy for such 

 as approximate to the following description. A strip of wool, 

 about i:') in. long and 1^, in. wide, has a neat handle shaped at 

 one end, occupying about 4 in. of the length, the remainder 

 forming the base upon which the slightly convex stropping 

 surfaces are built. 



Both the stropping surfaces should be of the finest Russia 

 leather. One side is usually charged with the stropping paste, 

 the oppo.site surface being left bare for finishing. Some strops 

 have the finishing side of buckskin, this we deem wrong for our 

 special purpose, as the velvety bufl: is apt to impart a rounded 

 ed"e to the razor. The longer the stroji has been in service the 

 better the results obtained, provided that its surfaces have not 

 been hacked. An old friend will have itsi-urfaces hard, .smooth 

 and glistening : care should be taken to keep it so. The 

 stropping paste should be applied very sparingly at remote 

 periods and with gre it care. Black paste should he avoided, 

 as it geneniU.y contains emery powder, the red paste is usually 

 of iron-oxide. Good ]>aste can be made by thoroughly mi.ving 

 the finest jeweller's rouge with the smallest quantity of tallow. 

 Never lay the strop down with either surface in contact with 

 the bench. Avoid belt strops, as the result in inexperienced 

 hands is a rounded razor edge. Holding our ideal strop in the 



