October, 1902.] 



KNOWLEDGE 



237 





Conducted by M. ICrpss. 



Pond-life Collecting in October. — October is one of the 

 best months for the poml-hunter ; the weather i.s cooler, the 

 ponds have become filled with rain-water agpiin, with plentj* of 

 food material iu the shape of flagellate Infusoria, and the 

 Crustaceans are on the decline. Iu this month the greatest 

 variety in species of Rotifera is usually found, )iarticularly of 

 the smaller and rarer kinds, and not infrequently thirty to forty 

 species may be obtained in one or two small ponds. As a 

 general rule one cannot e.xpect much variety when a few species 

 are present in excessive abundance. The following is a list of 

 forty-four species of Rotifers actually collected on one occasion 

 in three ponds on October 15th, 18",I8, showing what may bo 

 looked for : — Hosriilaria regalis, oriiata, cuniuld, timbii/iia, 

 edeiitata, and aiiiiulata ; Lhunuis anuulnlus, var. granulosus ; 

 OecisUs rrynlullinus ; Philodina megalotrocha ; Jlolijfcr rult/ari-i ; 

 .'iiinchaeta tremula and obloiiga ; Asplanclina priodonta ; 

 Xotops h'lptopu^ ; Puhjarthra platyptera ; Enspliura attriia ; 

 piircularia lotirfixeta. sterea, and forficuUi ; Primles felis : 

 Difjleiia biraphis; Mastigocerca rattua and bUonih ; Coelopux 

 purceUus and tenuior ; Patlulus bicornis ; Dia.ichiza exii)im ,■ 

 Diatyla Jiexilis ; }fo)Wst;ila lunaris ; Dimxharis pnciU'iii; 

 Stephnnnps himeUuris ; Cathypna luna ; Euchlaiiix aro/iha ; 

 .)[ft<i/iidiu ac u<it inula ; Brachmmis! angularis and baker! ; 

 J'oinijlmlyx sulcata; Sulholca labia and ncapha ; Aiiuraea 

 aiuleata, cochlearis, tfcta, hypclasnia, and xtipitattt. On the 

 other hand, the various kinds of Rotifers known as summer 

 forms will now have disapjieared. Pedallon mi rum is such a 

 form which may occasionally still be seen during a warm 

 October, but is then usually very scarce or absent. 



MicitoTOMES (cniilinued). —It is impossible to give descriptions 

 of all the different microtomes, even if one eliminates tho.se that 

 do not possess special merit or qualities. It will only be possible 

 to name two or three, and if further information is required 

 about them it can be obtained from any of the usual dealers. 



Leitz and Rcichert both make good .sound microtomes, the 

 latter having a high reputation for his continuously working 

 micrometer screw upon the rivet model. This continuous 

 working is brought about by simple means, viz., when the 

 screw has reached the limit of its movement, it is turned through 

 180° so that its opposite e.xtremity points towards the object- 

 bolder, when the working can at once be continued. 



The Minot microtome for the paraffin ribbou method, by 

 /imniermm, of Leipzig, is a very e.tcellent form, and Becker 

 also makes one ou the Schanze and Minot models. The former 

 is worked by rotating a balance wheel, whose rotary action is 

 changed into a vertical iuovement of the object slide by means of 

 acrankaction. When the object slide is moving upwards, a lever 

 strikes one of the spokes of the rachet wheel which, in turn, moves 

 the large toothed wheel of the horizontal micrometer screw, 

 thus advancing the object towards the knife ; it works with 

 great rapidity, and cuts sections up to 2 x 2" with exactness and 

 absolutely flat. 



The Reinhold Giltay model has points of both ingenuity and 

 orij;inality ; it is constructed for the paraffin process. It is 

 mountea upon an iron stand with a wooden cover, in a similar 

 manner to a sewing machine; the working parts are com- 

 pensated for wear and tear, aud it is constructed on simihir 

 principles to the Minot from which it differs in the feed 

 adjustment. This is effected by tbe slide of the knife block 

 towards the object by means of a micrometer scrrw passing 

 through the block, the movement of the object being restricted 

 to the vertical direction. 



The microtomes of Schanze, of Leipzig, have many features 

 which may fairly claim for them special attention and favour ; 

 they are second to none in accuracy and beauty of workmanship, 

 and are unexcelled for general utility. 



In order to do work with the microtome, there is certain 

 accessory apparatus which is necessary, and on which will 

 materially depend the success or failure of the early experi- 

 ments. Knives will have to be selected, and the beginner will 

 find a bewildering number of patterns from which to make his 

 choice. For general paraffin cutting with sledge microtomes, 

 the Henking pattern knife, having a blade 6 cm. long and the 

 handle i) cm. long, is probably the best. Jung's pattern, in 

 which the blade fits into an ebony screw handle is another 

 useful form. It may be employed for cutting at right angles 

 to the microtome guides or obliquely, with a slicing cut, pro- 

 vided that the knife is of suitable size for the microtome. 



Other patterns in use are Weikert's, with a straight handle, 

 and both sides of the blade concave for cutting celloidin 

 embedded objects under fluid : and Thomas, or the Heidelberg 

 pattern, with a curved handle having the underjide flat and the 

 upper side concave. The latter does the same work as the Jung 

 pattern already referred to, but does not require a special 

 holder, as it fits directly to the carrier of the microtome. 



The sharpening of the knives is a very important process, 

 and, excepting this is carefully attended to, it is utterly impos- 

 sible to cut good sections. Some brief instructions on these 

 matters appeared in Knowledge, July number. 



A few words may be added to emphasize the necessity for 

 the proper preservation of the objects that are to be cut into 

 sections. Living organisms or parts of them must be taken at 

 the time of robust health and killed and fixed instiintaneously, 

 with the substances best suited for obtaining the desired results. 

 All the fixatives known to science will not preserve the lifelike 

 stages in the histology of the subject when once post-morlcin 

 changes have taken place. The subject of fixing, embedding iu 

 celloidin and paraffin, staining en bloc, and mounting generally, 

 are so fully treated in books on these specific subjects that the 

 space available in this journal will not admit of treating each 

 of the processes in detail. 



There is one imjiortant point, however, with regard to paraffin 

 for embedding ; different writers disagree as to the melting point 

 of the wax that should be used ; as a matter of fact, all grades 

 are useful, and the melting point of the paraffin will depend on 

 the temperature of the laboratory in which the work is done and 

 the thickness of the sections required. If the room is 1.5" C, 

 and sections are required lU «■ thick, paraffin with a melting 

 point of 46° C. will be suitable; but for sections ;'>;"• thick 

 with the same room temperature, a higher melting pjint of 

 paraffin must be employed, say, 48° C. or oO" C.,and for sections 

 1 fi thick, and the same room temperature, the wax must have 

 a still higher melting point, and rice rersd. 



If the paraffin is too soft for tbe temperature of the work- 

 room and thickness of sections, then the sections will probably 

 crumble together ; if the paraffin is too hard the sections will 

 curl or roll upon the knife. 



System in this work, as in everything else of so precise and 

 delicate a nature, is the one importaut thing : nothing must be 

 done in a hurry, but every stage carefully arranged for and 

 anticipated. 



Practical Scheme. — Through the courtesy of a reader we 

 are able to offer to such as may wish to avail themselves of it, 

 material for distribution. 



It consists of Rasal Reef Rock, containing a variety of 

 organisms living iu comparatively shallow tropical waters, 

 probably in Pliocene time, as well as interesting inclusions of 

 the older oceanic beds: — tJlobigerina in rock; Radiolaria in 

 rock ; Diatoms in rock. These should properly be ground for 

 microscopical examination. 



The supply is not a very extensive one, but it is of special 

 interest, and will be forwarded to applicants on receipt of 

 stamped addressed label, together with the coupon wluch will 

 be found in the advertisement pages. 



NOTKS AND QUERIES. 



./. S. — -The light-dispersing power of the glow-worm has been 

 attributed to several causes. It was at one time thought to Ix^ 

 caused by |)hosphorous, but this theory has not been confirmed 

 by later researches. Some experiments have been conducted 

 by a French naturalist, who proved that the illumination is used 

 as a means of .signalling between individuals of the same species. 

 He placed a glow-worm in a glass tube, but it emitted no light 

 until others of the same species approached ; then to attract 

 their attention it emitted jets of light in rapid succession. 



