May, 1011. 



KNOWLEDGi:. 



193 



Now the index of visibility or power of seeing an unstained, 

 and presumably a stained, structure is greater when the 

 medium has a very low or a \'ery high refraction index. 



Bacteria would be invisible in a medium having a refraction 

 index of 1-55, in Canada Balsam they would be seen, in 

 Parolein they would be seen much better, and this theoretical 

 statement is borne out by experience. V'ery delicate structures 

 like the flagella of bacteria are better seen in Parolein than in 

 Canada Balsam. 



Mr. E. M. Nelson and Mr. Merlin both state that the 

 delicate structures, in some bacterial films I sent them, "are 

 strong and sharp ; in fact, stronger and sharper than in balsam.'' 



I am not prepared to state that there is no better mounting 

 medium than Parolein : I should only be too glad to hear of one 

 that offers a reasonable chance of permanency and which has 

 as good optical (jualities. All I can say is that at present 

 every slide that has a place in my cabinet will be mounted in 

 Parolein ; Canada Balsam has ser\'ed me very badly. 



Alfred C. Coles, M.D., D.Sc, F.R.S. (Edin.i. 



M.R.C.P. iLond.l. 



THE MICROLOGIST.—We have received from the 

 publishers, Messrs. Flatters, Milborne tt McKechnie, Ltd., of 

 Manchester, Part 4 of their quarterly journal. TIic Micrologist. 

 In this part full details are given for the preparation of slides 

 illustrating the Marine Protozoa, chiefly the Radiolaria — such 

 types as Sphacrozoum, Anlacantlia and My.xosphaera being 

 dealt with ; in the latter case the method of infiltrating and 

 cutting sections of the colony being described. The Amoeba, 

 its life-history, structure, cultivation and the preparation 

 of microscopical mounts, is dealt with by Mr. Gordon 

 McKechnie. It would be an advantage if some indication 

 were made as to what other organisms can be treated in the 

 same manner as that described for Amoeba : for instance, 

 would the same treatment suit Paraiiiocciunt, Stcntor, and 

 so on ? Included in this number are formulae for stains 

 and mounting media, which cannot fail to be of use to 

 the working microscopist. Plate IV illustrates the objects 

 dealt with and of the slides sent out with this number we 

 have received two — Amoeba and Sphacrozoum — the latter 

 making a very pretty object with a low-power and dark- 

 ground illumination. 



QUEKETT MICROSCOPICAL CLUB.— March 28th, 

 1911. Professor E. A. Minchin. M..A., President, in the chair. 

 The death of Mr. \V. M. Bywater, F.R.M.S.. on March 1st. 

 was announced. He was one of the fovmders of the Club, and 

 its first secretary. — Mr. A. C. Banfield exhibited and described 

 a new quartz mercury \'apour lamp, manufactured by the Brush 

 Electrical Company. The cjuartz tube used in the new form 

 is about four inches in length. The lamp is extremely rich in 

 ultra-violet rays, and will sterilize a Petri-dish cultivation in 

 less than one miimte. The peculiar mercury spectrum gives a 

 unique opportunity of easily obtaining strictly monochromatic 

 light in large ijuantity. with a choice of several wave-lengths, 

 that at X 5461 being the most powerful source of monochromatic 

 light at present available. — Mr. E. M. Nelson. F.R.M.S., 

 described the best method of obtaining dark-ground illumina- 

 tion. Place the buU's-ej-e at right angles to the edge of the 

 flame. Adjust its height so that the horizontal optical axis of 

 the bull's-eye cuts the brightest part of the edge of the flame. 

 Focus the bull's-eye so that a sharp image of the flame 

 is thrown upon a wall, distant, say. five feet. Place the 

 lamp, without altering these adjustments, on the left-hand side 

 of the microscope, and ten to twelve inches from the mirror ; 

 remove substage condenser and objective, and place a low- 

 power eyepiece in position. Incline the plane mirror and 

 adjust the height of the lamp so that the bright part of the 

 flame falls centrally upon it. Then incline the mirror so that 

 the full beam is reflected up the microscope tube. From 

 a distance of six or eight inches look at the bright spot of light 

 at the eye-lens. This should be an evenly-illuminated bright 

 disc. Replace condenser and objective, centre and focus 

 substage i[i usual manner and proceed with the work in hand. 



selecting a suitable black stop, one not too large, and a dark 

 field of maximum brightness for that set of apparatus will 

 have been obtained. To obtain tn- darkest possible ground 

 many objectives require the tubs-i^iigth to be increased, 

 sometimes considerably. Mr. C. Ls2j dirties exhibited, at 

 Mr. Nelson's request, the lamp and condenser described. — 

 Mr. A. A. C. Eliot Merhn. F.R.M.S., disca^,sed "Some New 

 Diatomic Structure discovered with a nev/ Zeiss apochromat." 

 — Mr. James Murray, F.R.S.E., F.Z.S., read a paper, "Water 

 Bears or Tardigrada." As the name Tardigiada is already 

 appropriated by vertebrates the group is now classified as 

 order Arctiscoida, family Xenomorphidae. The paper 

 describes four new genera and their relationships, concluding 

 with a synopsis of the ten genera and one hundred and 

 twenty species at present admitted. — Mr. M. Ainslie exhibited 

 and described a " finder " for the microscope, useful with 

 powers up to about one-sixth of an inch. It consists of a 

 hinged and pointed arm clamped to one corner of the stage. 

 When it is wished to record the position of an observed object, 

 the point is inked and allowed to make a mark on the label to 

 the left of the object. It is intended for use with either a 

 mechanical stage or sliding bar. 



ORNITHOLOGY. 



By Hugh Boyd W.att, M.B.O.U. 



BIRDS FROM NEW GUINEA.— The newly arrived 

 collection referred to in the last number of " Knowledge " 

 was shown in the Board Room of the Natural History 

 Museum. South Kensington, on the 5th April, and The Times 

 of the following day gives a brief report on it. The collection 

 includes eleven species and several dozen specimens of Birds 

 of Paradise and their congeners of the crow and starling 

 group. There are nine examples of the magnificent flame- 

 coloured Bird of Paradise {Xanthoinelas ardciis) hitherto 

 represented in Europe by only two specimens in Holland and 

 an imperfect skin in Genoa. Amongst the larger birds is an 

 ibis (much like the sacred ibis), and, in addition to the more 

 distinctively tropical kinds mentioned last month, one or two 

 sheldrakes and ducks. A familiar British bird occurs in the 

 form of a young male common cuckoo taken in December 

 last, presumably on migration from northern regions to 

 AustraUa. The collection is very rich in the groups of smaller 

 birds. The genera best represented are sunbirds, flower- 

 peckers, honey-eaters, and flycatchers, also cuckoo-shrikes, 

 ground-thrushes and bee-eaters. The material will enable 

 the distribution of many species to be worked out better than 

 hitherto ; and results of even more importance are anticipated 

 from the regions of the great snow mountains which the 

 expedition hopes to attain, and where the avi-fauna is far less 

 known than in that part of Dutch New Guinea from which the 

 collection now under re\^iew has come. 



A BLACK EGG.— In Tlie Field of 25th March last, an egg 

 uniformly black in colour is figured, sent by a correspondent 

 from his duck-house, where ordinary wild ducks and others 

 called by him "East Indians" are kept together. The last- 

 named are described as black, with bottle-green on the wings 

 and hackles, and are probably the Cayuga duck, which comes 

 from South America. It is explained that eggs of this 

 melanistic variety of duck sometimes partake of the colour of 

 the plumage, but the black colouring does not penetrate the 

 shell, being due to an oily pigment which can be rubbed oft'. 

 After successive layings the colour fades and eventually 

 disappears. 



A NOVEL BAIT FOR WOOD-PIGEONS.— Intoxicants 

 have recently been recommended and tried as an assistance 

 in getting rid of the wood-pigeon pest. Mr. J. L. Courthope, 

 M.P., suggests that corn be soaked in spirit and distributed in 

 the feeding places of the birds, which will eat the grain, 

 become intoxicated, and then be easily caught and killed. We 

 believe that gin has been used in some such way in Herts, 

 with efl'ectivc results. 



