Jni.v 2, 1900.] 



KNOWLEDGE 



1G5 



diflferencea of size and shape. An example convenient 

 for illustration is afforded by Eunjcope nov(Z-:eIandi<f, 

 Beddard. in which it will be seen that the fourth pair of 



Eurycope norce-zelandite, Beddard. From " Challenger " Eeport. 



limbs are about thrice as long as the seventh pair. The 

 generic name, signifying broad-oars, refers to the flatten- 

 ing of the penultimate and ante-penultimate joints in 

 the hinder set of limbs; and this widening of the blades 

 is carried in some species to a far greater extent than in 

 the one here figured. 



It may seem disproportionate to have given a whole 

 chapter to the Isopoda, which to some readei-s must still 

 seem an obscure, insignificant and unimportant order. 

 A whole chapter has only sufficed to indicate the barest 

 outlines of classification, the most obtrusive differences 

 here and there in habits and outward form. The 

 internal structure and the minutiae of the ever varying 

 mouth-organs have been left on one side, with much 

 else. The fact is that the explaining of all that is known 

 on the subject of this chapter would expand into a 

 volume, the exploring of all that is unknown might 

 occupy, amuse, and dignify a lifetime. 



i^tcroscopi). 



By John II. Cooke, f.l.s., f.o.s. 



At a recent meeting of the Manchester Microscopical Society 

 Mr. M. L. Sykes contributed a note on the methods that Mr. C. F. 

 Rousselet employs when preserving and mounting organisms so 

 that they shall retain their natural forms with their colours, 

 muscles, etc. Mr. Rousselet exhibited a number of micro- 

 scopical preparations of Rotatoria at the International Zoj 

 logical Congress at Cambridge, which claimed special notice for 

 their beauty and the success of the methods he had adopteJ. 

 Rotifera cannot be killed suddenly, by any known process 

 without contracting violently, and losing all of their natural 

 appearance. To kill and preserve them with their cilia fully ex- 

 panded and in their natural condition Mr. Rous.selet first narcotizes 

 them with a solution consisting of 3 parts of a 2 per cent, solution 

 of hydrochlorate of cocaine, 1 part of methylated spirits, and 6 

 parts of water. The Rotifers should first be Isolated in a watch 

 glass and clean water, and a drop or two drops of the solution 

 added at first, after five or ten minutes another drop should be 

 added, and afterwards drop by drop and very slowly until the 

 animals are completely narcotized. They may then be killed and 

 fixed by adding one drop of an eighth per cent, to a quarter per 

 cent, solution of osmic acid. To clear from the solution they must 

 be washed several times, and then transferred to a 2^ per cent. 



solution of formaldehyde, and should be mounted in this fluid 

 in hollow ground glass slips. The objects have all the appearance 

 of living animiils, the colours, internal structure, and outward 

 fonn being beautifully preserved in situ. 



The current issue ("Zoology") of the "Journal of the Linnean 

 Society " contains, among other articles nf interest to the micro 

 scopist, a contribution by Mr. H. Wager on "The Eye Spot anl 

 Flagellum of Knglena viridis,' and a paper by Mr. li. M. IJernard 

 on " The Structure of Pontes." 



In a record of observations on the microscopic life of Arctic 

 regions, Ur. Levin states that air from numerous localities showed 

 only a few moulds. In water from the sea-surface bacteria were 

 always found, but in very small numbers — perhaps one thousand 

 to a quart ; while water from glaciers, snow streams, ice and 

 melted snow, also gave evidences of bacteria in small numbeis. In 

 water from the deep sea these organisms were more abundant 

 than on the surface. With the exception of a single species of 

 bacterium found in one bear and two seals, the intestinal contents 

 of the white bear, seal, shark, eider duck, and other Arctic 

 vertebrates were absolutely sterile, but bacteria were almost in- 

 variably present in the lower marine animals. These observations 

 on germ-free intestines are of special importance and interest, as 

 they confirm the idea of Pasteur and a few others that bacteria 

 are not essential to digestion. 



It is a curious fact that among the impurities that have been 

 detected in calcium carbide are microscopic diamonds. These 

 gems are so exceedingly small as to be of no commercial value, 

 but they accentuate the fact that carbon in the crystalline con- 

 dition can be produced artificially, and give reason to the assump- 

 tion that some day it will be possible to produce diamonds of a 

 size sufficient to be marketable. 



In his Presidential address to the Quekett Society Dr. Tatham 

 alluded to the difficulties attending the use of realgar as a mount- 

 ing medium. Its high refractive index makes it most useful, but 

 its disadvantages are many and serious. The fusion of the 

 material which is necessary for the mounting process requires 

 the application of great heat. This liberates intensely poisonous 

 fumes, and frequently so distorts the valves of the diatoms that they 

 are seldom found to lie Hat on the cooling of the slide. The colour 

 of the finished mount is a deep yellow, and this seriously detracts 

 from the value of the mount for critical examination. This last 

 defect may be partially rectified by the use of suitably coloured 

 screens, of which a polished plate of bright blue glass has beaa 

 found to be best adapted in aiding in the resolution of difficult 

 tests. 



The Cambridge Scientific Instrument Company are introducing 

 an improved model of their well known rocking microtome. 

 Among the advantages that they claim f<jr the new form is the 

 possibility of cutting sections to any required degree of thinness 

 without the risk of the sections either varying in thickness or of 

 being torn on the upward movement of the object. 



In the epidermis of man and mammals Professor L. Ranvier 

 has recognised seven distinct layers, which are described to the 

 Royal Microscopical Society as stratum germinativum, fila inento- 

 sum, granulosum, intermedium, lucidum, corneum, and disjunctum, 

 in the order of their development. The limits are well defined, 

 each layer having distinct physical characters and chemical re- 

 actions. These layers are not formed by special elements, however, 

 and a cell originating in stratum germinativum becomes changed 

 and passes into stratimi fUamentosum and so on through the 

 series. 



Mr. J. E. Stead has recently jjublishcd the results of the work 

 that he has done on the microscopic structure of metals. E.xperience 

 has made it ea.sy to cut, grind, polish, and etch ordinary metals and 

 alloys, and specimens can now be prepared for the microscope in a 

 few minutes. Mr. Stead's work has yielded some unexpected results. 

 In a recent demonstration pig-iron was shown to have its con- 

 stituents gathered into separate centres, the carbides being in 

 isolated silvery cry.stals, while the phosphorus and sulphur com- 

 pounds were each distinctly separated. A brilliantly polished piece 

 of white pig-iron, containing carbon, sulphur and phosphorus, w-as 

 then heated until it became purple. Under the microscope the 

 constituents were found to have diverse colours, the iron being of a 

 fine sky blue, the carbides an orange colour, the phosphides a pale 

 brown yellow, and the sulphides a slaty blue. This method of 

 identifying phosphides is a new discovery which will be of great 

 value to iron manufacturers as a simple means of telling whether 

 iron contains phosphorus. The microscoije .shows that alloys, 

 instead of being homogeneous, as have been thought, are built uj) of 

 various ciystals, and is likely to prove of practical service to metal 

 workers in many ways. 



The acetylene flame may be rendered monochromatic by the 

 interposition of a screen of cobalt blue glass between the light and 

 the substage condenser. 



The principal uses of a light filter m photomicrography are for 

 the correction of the objective, the increase of contrast in the image, 



