22 



KNOWLEDGE. 



[January 1, 1901 . 



Conducted by 



Cross. 



Standard Sizes for Eykpieces. — On December 20th, 1890, 

 tbe Council of the Royal Microscopical Society adopted certain 

 internal diameters of draw-tabes as standards for eyepiece 

 sizes : withdrawing those which had been fixed by them in the 

 year 1882, which were two in number, viz. : '92 in. for small 

 stands, and 1-35 in. for large. 



The following were the sizes decided upon : — 

 No. 1, -9173 inch =: 23-300 m/m. 

 „ 2,1-04 „ =26-416 „ 

 „ .3,1-27 „ =.32-258 „ 

 „ 4,1-41 „ =3.V814 „ 



A year has gone by, and it is now possible to estimate the value 

 of these fresh gauges and to ascertain the probability of their 

 regular and general use. We are indebted to the courtesy of 

 manufacturers for statements of their intentions on the subject, 

 and although several have abandoned old sizes for the new 

 ones, or intend to do so, there yet remain some who do not 

 seem disposed to consult the public convenience by falling into 

 line. It will be apparent that Xo. 1 gauge is the one known as 

 the "Continental size," and is practically the same as the 

 smaller gauge recommended by the Royal Microscopical Society 

 in 1882. This is almost the universal diameter for student's 

 microscopes, and its popularity shows no likelihood of diminish- 

 ing. The No. 2 gauge is differently placed, and it is not 

 unanimously agreed that its inclusion in the list is either 

 necessary or advantageous. The number of microscopes in 

 which this is likely to be used is extremely limited. The No. 3 

 gauge is very suitable for stands of medium size, but No 4 is 

 of questionable value, for the day for the large models to which 

 this gauge would be applicable seems to have passed. All con- 

 sidered, it would seem that both the public and the manu- 

 facturers would have been better placed had three sizes only 

 been fixed, and in view of present knowledge and experience, a 

 confirmation of the sizes of 1882, with the addition of an inter- 

 mediate gauge, say the one of about 31 m/m., which was already 

 in regular use, would have been a verj' convenient and accept- 

 able range. The net result will probably be, as time goes on, 

 that gauges Nos. 1 and 3 will become tlie standards, and it is to 

 be hoped for the sake of uniformity that No. 2 at least may be 

 withdrawn. The fewer the number of gauges the better for 

 everyone. The prevailing tendency is to have a large tube, and 

 with a fitting at the eyepiece end to receive eyepieces of the 

 No. 1 gauge ; after all, if the body be of sufficiently large 

 diameter for photography, it does not matter greatly whether 

 the eyepiece be large or small, for only in the oculars of rerif 

 low power can a large field lens be used in the eyepiece. We are 

 informed that a general meeting of German microscope manu- 

 facturers is shortly to take place, and it is possible that some 

 consideration may be given to the recommendations of the 

 R. M. Society on the subject of both eyepieces and sub-stage 

 fittings. Universal sizes are of such prime importance that it is 

 to be hoped that the random system which has too long pre- 

 vailed, of every maker being a law unto himself, will be 

 unknown in the future, and as workers realise that the standard 

 sizes are an actual fact, they will insist on their incorporation 

 in their stands, and so induce those makers who might otherwise 

 be disinclined to alter the diameters of their tubes voluntarily, 

 to meet the exigencies of modern work l>y using only the 

 universal fittings of the lloyal Microscopical Sjciety. 



Blood Examination. — In recent years the examination of 

 blood for diagnosis of diseases, especially those peculiar to 

 tropical climates, has assumed great importance, and every 

 practical suggestion which enables it to be more thorougiily 

 performed is welcome. We have had sent to us the description 

 of a method devised by Dr. W. L. Braddon, of the Malay 



Peninsula, which is both interesting and effective. The cor- 

 puscles are examined in a film between (1) two square cover- 

 glasses joined together, or (2) a square cover-glass attached to a 

 '6 in. by 1 in. slide. Slides and cover-glasses are first of all 

 sterilized by the method recommended by Messrs. Pakes and 

 Howard, which is as follows :— The cover-glasses are dropped, 

 one hij line, into a 10 per cent, solution of chromic acid, contained 

 in an enamelled iron dish, and boiled for twenty minutes. They 

 are then tipped altogether into a shallow basin, and washed with 

 ordinary lap-water, until all trace of the yellow colour of 

 chromic acid has disappeared. The water is next poured off 

 and the slips are covered with rectified spirit. After this they 

 are washed in ab.solute alcohol, and handled with clean forceps." 

 These cover-glasses and slides are then dealt with as follows : — 



Method No. 1. — Two square cover-glasses are .accurately 

 superposed and firmly pressed together. An edging of vaseline 

 if for temporary purposes, or cement if for permanent purposes, 

 is laid over all the edges, except one, which is left free, and a 

 very small portion of that edge which is opposite to the 

 uncemented one. 



M^ethoil No. 2. — The cover-glass is placed on a 3 in. by 1 in. 

 slide in such a position that one of its edges exactly coincides 

 with that of the slide. It is then firmly pressed and vaseline 

 or cement is used, as mentioned in Method No. 1. 



Method iif Vsc. — A drop of blood is touched with the free 

 edge of the paired cover glass or slide, whereupon the blood 

 enters between the glasses in an exceedingly thin film, the 

 corpuscles being spread out with beautiful uniformity, and 

 having suffered a minimum amount of change from exposure 

 to air and none at all from handling or pressure. When the 

 blood film has entered, the free edge may be completely closed 

 and the examination made. Fresh blood keeps well under 

 these circumstances The advantages of these methods will 

 be obvious. A number of slides can be made up and stored 

 in a suitable air-tight bottle, and are always ready for use. 

 No special skill is required for the making of a first-class 

 blood-film. 



Comment.^. — We have tested this process practically, and found 

 that it was necessary to put the smallest possible suggestion of 

 cement between the covers before edging tliem outside, other- 

 wise the cement had a tendency to run in. When the blood 

 enters beneath the cover, so attenuated is the film that the 

 manipulator is apt to imagine that nothing is there, but, on 

 examination under a microscope, a beautiful single laj'er of 

 corpuscles is seen, spread out ready for examination. 



DissECTrxG WITH AN Erector. — The ordinary compound 

 microscope is not used as largely as it should be for dissecting 

 purposes, one of the special instruments designed for the work 

 being usually considered essential. As a matter of fact, any 

 monocular microscope having a draw-tube will serve well if an 

 erector be used. Nearly all the modern stands are fitted with 

 a thread of the universal size at the lower end of the draw-tube, 

 and into this the erector should be screwed. The objective that 

 will be found most useful in conjunction is Ijin. or 2in., and a 

 considerable variety of magnification can be secured by varying 

 the extension of the draw-tube, the object, of course, being seen 

 the right way up, and the tools, knives, &c., moving in natural 

 directions. The reason why the erector has not been recognised 

 as so useful an adjunct as it might have been, is probably 

 because unsuitable objectives have been used with it, but the 

 amateur preparer will be surprised at the great ease with which 

 he can do his work with the arrangement above mentioned. 



New AppaKatds. — It is proposed, instead of systematically 

 reviewing new appai'atus from time to time, to have a heading 

 for " Neir apparatus deseribed liji manufacturers," and opticians 

 who wish to notify the introduction of fresh accessories, 

 instruments, &c., will briefly state the details for insertion. 

 It is impossible to give a definite judgment on any item from an 

 examination of a single specimen, and the public being made 

 aware of the source of supply of such wares, will be better 

 able to judge of their suitability for their requirements by 

 communicating with the vendor, who would surely be pleased 

 to give full information on the subject. 



Notes and Querie.s. — Notes and suggestions will always be 

 welcomed from readers, and any assistance we can give by 

 replies to queries in these columns will be gladly rendered. 

 All communications for this column should be addressed to 

 M. I. Cross, Kno\vleiic;e Office, 326, High Holborn, W.C. 



