88 TIIK AMKKICAN MONTHLY [March, 



aiul acetic acid i> then atKlod until the Uc|ui(l is on tl)c point of 

 coajjuhitinjj. It is then phiccd in a copper tul)c tajierin«j at the 

 l><)tt(>iii, ami tliis tnhc is inserteil in the centrihijijal niacliine and 

 turned at the rate ot" ^,(kx> revohitions per minute lor 15 niiiuites. 

 TI1C l>acilli coMect at tlie narrow end ot" tlie tul^e. to»jether with 

 other sediment ami tliit. Tiie litpiid is poured oM". and the 

 sediment examined microscopicallv. 



Another. Thoiner's metlu>d. is this: 20 c. c. of suspecte<i milk 

 are mixed with i c. c. of 50 per cent, potash solution and heated 

 in a hath of Ix^iiinj; water until the tat is saponified, when the 

 solution turns \ellowish hiown. Hy this treatment the casein 

 ami alhumen become soluhle in acid. Add 20 cubic c. c of acetic 

 aciti, sliakc the solution, heat on water-bath lor 3 minutes, trans- 

 fer to a stronj; J^hiss tube and turn in the centrifu}j;al machine for 10 

 minutes. Tiu' liquid is then poured otV and the sediment is 

 washetl by shakinjj with 30 c. c. hot water, and again turned in 

 the centriiufjai machine. The water is poured oil" and the sedi- 

 ment placed upon cover-jjlasses. which are treated in the ordinary 

 way, staininj^ with hot Neclson solution. decolori/.in<f in 2^% 

 sulphuric acid, and Hnally staininj^ in metln lene-blue. Insteatl 

 of washing the cover-glasses in sulphuric acid, Thoiner simply 

 uses a solution of methylenc-bhie containing sulphuric acid. — 

 Nature, Jan. 12. iSy;^. 



To Mount Fish-Scales. — In piepanng fish-scales as trans- 

 parent slides lor examination l)v jiolarized light, or with a black 

 l>ackground, thev are usually mounted in Canada balsam to ren- 

 tier them transparent, but this means of mounting gives a dull 

 and nuuldy image ; their appearance is greatly improved by 

 mounting them in a mixture, half alcohol and half water, the 

 image is nrighter and clearer, and the colors with polarized light 

 and a selenite plate much more brilliant. 



By using a Herapathite him mounted as the analy/.er the 

 image is verv much brighter, and the colors stronger when using 

 the selenite than with a Xicol eyepiece ; but without the selenite 

 plate the Held gives only a dull lirowii color, instead of being a 

 deep black, as with two Nicols. 



It is verv desirable that the scales should be perfectly clean and 

 free from the slime that adheres so obstinately, especially in such 

 scales as have strong spines, as the sole, perch, etc. Tlie scales, 

 when possible, should be gently detached from the fresh skin, be- 

 ing careful not to break oHany of the spines, and cleaned by 

 steeping them in warm water and gently brushing oH' the mucus 

 with a camel's-hair brush ; but if this does not succeed in perfectly 

 cleaning them they should be digested for some hours with pep- 

 sin, when they can be thoroughly cleaned. As it is dillicult to 

 find a means of fixing the scales to the slide when mounting in 

 spirit, the cells should be made in the turn-table with asphalte 

 to such a depth that the cover-glass when mounted will hold 

 them wit!-, a slight pressure. — No ^ig. Paris. 



