70 



KNOWLEDGE. 



[March 1. 1899. 



By John H. Cooke, f.l.s., f.g.s. 



A tough cement, suitable for use with the thinnest of rock- 

 sections, may be made by heating together for some time sixteen 

 parts by weight of Canada balsam and fifty parts of shellac. 



Distilled water should be used in the treatment of microscopic 

 objects on all occasions, as, on the evaporation of ordinary water, 

 crystalline salts may be deposited on the object. 



To remove an excess of balsam from around a cover-glass, 

 allow the balsam to become hard and then chip it away with the 

 edge of a blunt knife, taking care to avoid touching the cover- 

 glass during the operation. A tooth brush dipped in methylated 

 spirits will then readily remove what is left. Finally, dry and 

 polish the slide with Japanese filter paper. 



Specimens of plasmodia, for the study of the myxomycetes, 

 may be obtained from the sclerotia which is to be found attached 

 to rotten wood or on the ground beneath old logs. To prepare 

 these, Mr. M. Barber, of Kansas University, suggests that pieces 

 of the material should be placed in a warm moist place. After 

 a few hours the plasmodia will develop, and they may then be 

 fed with rotten wood or fleshy fungi. Small plasmodia, for the 

 demonstration of protoplasmic currents, may be obtained by 

 ])utting pieces of sclerotia in a hanging drop of water, or by 

 placing in a large cover-glass on a plasmodium and transferring 

 it to a moist cell after the plasmodium has run over it. 



Kleinberg's picro-sulphuric acid is recommended for fixing 

 zoophytes and polyzoa with their tentacles extended. The 

 specimens should be placed in water, and as soon as they extend 

 themselves they should quickly be covered with the solution. 

 Fixation follows rapidly, when, after immersion in the usual 

 grades of alcohol, they may be stained with any ordinary stain. 

 Picro-carmine gives the most satisfactory results. 



Formalin is now largely used in most laboratories as a 

 preservative and fixative re-agent. It does not interfere with 

 the processes of staining to any appreciable extent, nor does it 

 cause much shrinkage of the structures operated on. Both as 

 regards ease of manipulation and expense, it is decidedly superior 

 to osmic acid. 



A novel method of illumination, for the investigation of the 

 structure of diatoms, is suggested by Mr. Allan Dick in his 

 " Notes on the Polarizing Microscope." A thin platinum wire 

 is twisted into a loop of just sufficient size to allow of the 

 l)assage of a darning needle. This wire is rendered incandescent 

 by a spirit lamp or a Bunsen burner, and it is placed at a distance 

 of eight inches from a condenser in such a manner that the loop 

 may be at right angles to the axis of the microscope tube. The 

 most favourable condition for using this source of illumination 

 is when the image of the loop may be seen in the field of view 

 just surrounding the object. In some cases it is better to use 

 a triangular rather than a circular loop, so as to minimize the 

 risk of mistaking circular effects. 



To preserve for an indefinite period such fluid mounts as 

 fish embryos, ova, and the like, it is necessary to use a cement 

 having exceptional strength and fluid-resisting properties. The 

 following cement is admirably adapted for this purpose. Take 

 two parts of carbonate of lead, two parts of red oxide of lead, 

 and three parts of litharge. Grind these very finely, mix them 

 dry and keep in a wide-mouthed bottle. When required for use 

 a little of the powder should be mixed with old gold size on a 

 watch glass. It is necessary that there should be no trace of 

 gi'it or unground matter in the mixture. A cell made with this 

 cement may be tiled off the glass slip without the cell breaking 

 away. 



In a paper recently read before the Manchester Microscopical 

 Society, Mr. J. V. Wolstenholme, F.it..M.s., gives details of the 

 methods that were employed in his investigations on the micro- 

 cocci (Botriomyces), which produce tumours in domesticated 

 animals. He removed from the groin of a horse a pear-shaped 

 tumour, the mass of which was dense, firm, and resistant, and of 

 a pale pink colour. In the centre was an abscess cavity, two 

 and a half by one and a half inches, which communicated by 

 narrow channels with a large sore or ulcer at the base of the 

 tumour. For microscopical examination, portions of this tumour 



were hardened in (a) Miiller's fluid, ((3) picric acid, (7) alcohol, 

 after which they were easily cut with the freezing microtome, 

 and stained readily. In some cases it was found to be an 

 advantage to embed the portion of tissue in celloidin before 

 cutting. The .stains used were (a) picro-carmine, (/Jj hsematin 

 followed by picro-carmine, (V) hajmatin, and then rubin and 

 orange combined, (S) the Plantz method. Of these, the hsematin 

 with rubin and orange gave the most perfect differentiation. 

 The fibrous tissue was thus stained pink, and the nuclei purple. 

 It was in the nuclei, which appeared as minute specks in a 

 delicate fibrous growth, that the colonies appeared. Under the 

 one-sixth objective a colony was seen to be made up of grape- 

 like bodies, some of a pale orange, and others of a pale green 

 colour, but under the one-twelfth inch oil immersion the grape- 

 like bodies were seen to be filled with cocci — small round 

 elements — which were about 3 (it diameter. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.b.a.s. 



CriASE's CoMF.T. — This comet, which is remarkable as having 

 been discovered by photography in the position of the radiant 

 point of the Leonids on the very night when a shower of these 

 meteors was expected, is receding from the earth and becoming 

 perceptibly fainter. On IMarch 4th its apijarent brightness will 

 be 0"75, or three-fourths the amount it exhibited at the time of 

 discovery. The comet is moving slowly westwards in the region 

 between Leo Minor and the southern limits of Ursa Major, 

 and its position on March 4th will be R.A. lOh. .54m. 31-4s., 

 Dec. + 38° 10' 40". It will be distant from the earth about 

 one hundred and ninety millions of miles. The latest com- 

 putations of the orbit show that the observations are satisfied 

 by parabolic elements, and that there is no probability that the 

 comet is identical with Comet 1807 I., as has been suggested. 



Wo[.f".s Comet. — This object remains faintly visible in large 

 instrumeuts, and is situated in the south-west part of Monoceros. 

 On March 4th it will be separated from the earth by an interval 

 of two hundred and seven millions of miles, and its apparent 

 place will be R.A. (jh. Pim. iMs., Dec. —8° 8'. The comet is 

 moving slowly to the N.E., and is not likely to be visible much 

 longer even in the best telescopes. 



The Recent Shower of Leonids. — Reports of this display 

 continue to come in, and show the very widespread interest 

 manifested in the phenomenon. That this interest will be 

 further accentuated next November is certain, seeing that the 

 outlook is more promising as regards a really fine display. The 

 moon, it is true, will be nearly full, and must, in any case, rob 

 the event of much of the imposing eifect it would have presented 

 on a dark sky ; but if the shower returns in its full strength it 

 will, even in the presence of unfavourable circumstances, prove 

 a striking spectacle. Many of the Leonids are bright meteors, 

 quite equal to first magnitude stars, and will be distinctly visible 

 in moonlight. The observations in 1898 have been of decided 

 value in several connections. The photographs, taken in com- 

 bination with the naked eye observations, jirove that the radiant 

 is in about R.A. 151", Dec. 22 '.3'. The results also prove that 

 the earth did not really encounter the main body of meteors, 

 but only a tenuous region of the stream far in the van of the 

 parent comet. The estimates of the time of maximum seem to 

 have differed at various places, as though locality affected the 

 visible numbers in some degree. In the case of a comparatively 

 feeble shower such discordances are sure to occur, as the 

 methods of observers, the number employed, the suitability of 

 their positions, and other circumstances affect the results. In 

 any case, the recent shower of Leonids was certainly most 

 numerously presented after sunrise in England, so that even had 

 favourable weather backed up the efforts of observers in this 

 country, the phenomenon would have been one of decidedly 

 minor importance. 



Meteors and the Si'rini; Season. — Very few meteors are 

 usually observed in the spring season ; in fact, as regards these 

 objects, it may be considered as the most unproductive time of 

 the year. Fireballs, however, occasionally appear, and provide 

 valuable materials for discussion. On January 26th a very fine 

 meteor was seen at 8h, .'lOm. p.m., by Mr. She])pard at Bishop 



