Jascasy, 1901. 



KNOWLEDGE. 



21 



Quilter on " A ilethod of taking; [uternal Casts of Foraniinifera," 

 which should prove useful to students, iiud might bo capable of 

 extended application. 



AVatsox's ■■ Akhcs" MicROscoi'K. — .V cheap microscoiie may 

 generally be looked ujion with suspicion, but Messrs. \V. Watson 

 & Sons have just brought out a new microscope, which is not 

 only cheap but of excellent workmanshi]i. The de.siL;n has 

 several novel fejitnres. The limb is rigidly att.achad.to the 

 stage, as in all Messrs. Watson's models, but the tine adjust 

 ment is of the direct-acting micrometer screw type, actuated by 

 an inverted head placed beneath the limb. The coarse adjust- 

 ment is by means of a diagonally cut pinion which engages 

 directly in the threads of the screw of this fine adjustment, 

 there being another supporting wheel on tlie other side, so that 

 one slide serves Ixith for coarse and tine adjustment. The foot 

 is of the tripod pattern with a spread of nearly 7 inches ; the 

 body is inclinable ; the stage is ^\ inches square ; and the body 

 is provided with a draw-tube giving a variable tube-length of 

 from ,5A to '.1 inches. The eyei)ieces arc the R.JI.S. standard 

 Continental size, i.e., itlT.S inch. There are adjustable double 

 mirrors, and a ring beneath the stage of the E.M.S. sfcvndard 

 gauge, for condenser, I'cc. Compensating screws are provided 

 for the working parts of the microscope. For this particular 

 microscope Messrs. Watson have introduced a new series of 

 objectives at specially low prices ; but of these I shall have 

 more to say when 1 have had an opportunity of examining them 

 personallj-. 



New Methoii of Mounting; Rotifkks. — I have recently 

 seen some Rotifers mounted by a method which appears to me 

 to have several novel points. The Rotifers, which were of the 

 genus Megalotror/ia, are now more than two years old, but are 

 as bright and clear a.s when first mounted. They were jiut up 

 by Mr. W. Brockett, Laboratory A.ssistant in the Zoological 

 Laboratories at ('ambridge, and I am indebted to him for the 

 following explanation of his method. A few living Rotifers 

 are put in a large drop of water on an ordinary slide. They are 

 then narcotised by the addition to the water of a very few 

 granules of cocaine. When perfectly extended, after examina- 

 tion under a lens or a microscope, a drop of two per cent, 

 osmic acid is placed on a clean cover-glass, which is then rapidly 

 inverted and as quickly lowered on to the Rotifers. Actual 

 contact, and therefore compression of the animals, is prevented 

 by small pieces of gum label being stuck on the slip at each 

 corner of the cover-glass, so as to make four small supports. 

 The osmic acid is allowed to remain from one to three minutes, 

 the progress of the staining being carefully watched under the 

 microscope, after which distilled water is run under the cover- 

 glass by the " irrigation " method. This is merely the ]ilacing 

 of a small quantity of the irrigating fluid at one side of the 

 cover-glass and applying a piece of blotting paper to the 

 opposite side, bj- which means a current is .set up and the fluid 

 drawn under the cover-glass. By the same method of irrig.i- 

 tion, picro-carmine is then also drawn under, and allowed to 

 stain for ten to thirty minutes, the progress of the staining 

 being carefully watched as before. Finally, by the same 

 method, there must be gradual dehydration with 30 percent., 

 50 per cent., 7lt per cent., and 90 per cent, alcohols in the order 

 given, after which follows clearing with the usual clearing 

 agents, and mounting ("still Vjy the same method of irrigation) 

 with balsam dissolved in absolute alcohol. The slides will then 

 appear of a milky opacity, and be apparently useless, but should 

 be put aside for twenty-four hours, when they will become 

 clear and limpid. This clearing-up can be hastened by the 

 application of moderate heat, but the risks are manifold. It 

 will Vje noticed that an essential ])art of this method is the non- 

 disturbance of the Rotifers from the time they were narcotised, 

 and the drawing between cover-glass and .>'lip, of all the staining 

 and dehydrating re-agents, and of the mounting medium, by the 

 method of irrigation. 



MlcEO.scopiCAi- M.\TF,RIAL. — By the kindness of Mr. C. S. 

 Ponlter, of Wallington, I am able to ofl'er to the microscopical 

 readers of KnowleiiOE some leaves of /Miit^iu snihrii, showing 

 stellate hairs, and of KIa(afinu< ediilin, showing peculiar scales. 

 Those who desire to avail themselves of this material, should 

 send me a stamped addressed envelope, together with the coupon 

 appearing in the advertisement columns of this journal. 



NOTKS AND QUERIES. 



C. Judnoii. — There is no reason why the numerical aperture of 

 suhstage condensers as well as of objectives should not he 

 determined by the method described in Knowliuiue of 

 November last. It should be borne in min<l, however, that the 

 essential value of a condenser lies loss in its total aperture than 

 in the aplanatic cone which it is capable of transmitting, namely, 

 in that portion of its cone of light which is properly corrected. 

 Thus the Abbe form of chromatic condenser with a numerical 

 aperture of 1'-' or 1'4 N.A. has an aplanatic aperture of not 

 more than •.'<, whilst the recent English achromatic condensers 

 of 1 N.A. have aplanatic apertures varying from 9 to -dC) N.A., 

 and immersion condensers of 14 N.A. may have apl.anatic 

 apertures as high as IH N.A. An objecti%'e is a comjdicated 

 combination of lenses, so that the rules by which the focal 

 length of a single lens may bo determined do not apply to it, 

 but what you probably require is not the focal length so much 

 as the approximate equivalent focus, or, more definitely, the 

 initial magnification. I hope to have a note dealing with these 

 matters in the next issue of this Journal. 



I'liirer of Luroiitotioii ill Lophoptis rrj/stalliiiii.-<. — Mr. Willoughby 

 Dade, of 13, Northbrook Road, Dublin, writes : - " There seems 

 to be a division of opinion as to whether Lnjilinpiis /■ryslalliiitiK 

 has power of locomotion or not. Indeed, most authorities say 

 it has not. I have been keeping some colonies in a ten-inch 

 Ijell-jar for some time, and am confident that they have this 

 power. A short time since a group of about twenty individuals 

 divided, and three or four days later the two colonies were fully 

 a third of an inch apart, and now they are on different branches 

 of a piece of milfoil. I find all the fresh-water Polyzoa in the 

 Royal Canal here, excepting Alci/miella, which Allman says does 

 not inhabit Ireland. Liijihuinix does very well in confinement, 

 Crixtatflld only fairly well, but 1 am not successful with the 

 tubed genera such as Pluiiititello repi'iix, I'dliulicidld, and 

 Fre<lericeUa. These do not thrive, partly, I fancy, because 

 Cyclopia appears to be fond of picking the polypides out. I 

 should be very glad to know with what success other pond- 

 hunters keep these animals in captivity." 



Ij. B. — It is exceedingly difficult to indicate the subjects, 

 which would be likely to prove most interesting to you, in 

 which the microscope could be used. There is so large a range, 

 and every department dealt with intelligently provides such 

 varied and interesting material for study and observation, that 

 a knowledge of personal tastes and inclinations would be desir- 

 able before recommending. In the " Knowledge Diary " for 

 19l)4, obtainable from the publishers of this Journal, is an 

 article entitled " Some Uses of the Microscope," which might 

 prove of interest to you. It might be that on reflection you 

 would prefer some other instrument, such as a telescope, in 

 which case you would find the Diary referred to exceedingly 

 valuable, for it contains : " The Heavens for 11)04," " An Astro- 

 nomical Summary," " Practical Work of a Small Telescope," and 

 other scientific information. 



T. Webster. — The publisher of Knowledge, to whom I have 

 handed your letter, will lie able to inform you of a likely place 

 to obtain a talde similar to that described by Mr. Morgan. The 

 de.scription and illustration were intended to aid those who 

 were interested in getting such a device constructed locally, 

 but so many readers have enquired for a .source of supply that 

 the publisher has taken the matter in hand. 



./. ./. .Macdoiiald. — It would be impossible to give any explicit 

 direction as to the sizo of stop required to produce a black 

 background without knowing the condenser and objective that 

 were to be employed, together with the numerical apertures of 

 both. It is likely that you are attempting to obtain a black 

 background with an olijective possessing t<io large an N.A. 

 Except the aperture of the objective be cut down, it is not 

 convenient to obtain black ground illumination with numerical 

 apertures in excess of '75. 



Communications and enquiries on M^icroscopical matters are 

 cordially invited, and should be addressed to F. Snii.l.INOTON 

 ScAi.KS, "Jersey,^' St. Barnabas Jiaad, Caiiiliridije. 



