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HARDWICKE'S SCIENCE-GOSSIP. 



MICROSCOPY. 



Finishing Micro-Slides. — I have read the sen- 

 sible remarks of Mr. Ford with interest, and quite 

 agree that Canada balsam dissolved in benzole makes 

 a good cement for finishing purposes when no 

 coloured rings follow. If, however, coloured cements 

 are used on Canada balsam (as is the practice with most 

 mounters of the present day) there is considerable 

 risk of the benzole (which all these coloured cements 

 seemed to be made with) softening the balsam ring 

 and insinuating itself beneath the cover : at 

 least this has been my experience after using it — 

 and also the same occurs with dammar dissolved in 

 benzole. I have mounted a very large number of 

 slides, and have tried all cements recommended to 

 prevent running in— with more or less success. What 

 is wanted for the first coat is something that does not 

 easily dissolve the balsam. Some short time since a 

 small pamphlet fell in my way, published by Mr. 

 Ward of Manchester, being a paper on Mounting read 

 before the Science Association at Manchester, where 

 the author recommended a " brown cement " or anti- 

 running-in cement. I wrote for a shilling bottle. 

 I have given it an extensive trial and have found it 

 to supersede all other cements that 1 have tried. 

 The solvent used has evidently little or no effect on 

 balsam, and dries hard in five or six hours, when 

 coloured cements to any thickness may be added. I 

 have tried it immediately after mounting an object in 

 benzoled balsam with equal success. It is also a 

 useful cement for cementing covers in dry mounts, 

 being very adhesive and drying quickly. I can 

 strongly recommend it to all who are in want of a 

 good cement to prevent other cements running in. 

 — H. Mictiro, Lyme Regis, 



Ambiguous Phraseology.— I should feel ob- 

 liged if any of your readers would inform me what 

 is the numerical equivalent of the following expres- 

 sions (which I observe in many works on Microscopy), 

 viz: "enlarged," "much enlarged," "very much 

 enlarged," "magnified," " much magnified," "very 

 highly magnified ? " A moment's thought will reveal 

 to every microscopist the ambiguity and vagueness 

 of such terms, and the desirability of employing 

 some more precise mode of expressing the difference 

 between the magnified sketch and the natural size of 

 the object. The difficulty can easily be surmounted ; 

 all that is needed being, either a statement of the 

 linear magnificator represented by the sketch (if it be 

 drawn to scale) ; or, an indication of the focal depth 

 of the object glass and number of the eyepiece used. 

 Thus, it would be little trouble to add to the descrip- 

 tion of any sketch such words as : " 300 linear," or 

 " \ in. No. 2 e.p.," or " 1 in. No. 3 e.p." If this were 

 done, it would, I believe, much facilitate the work of 

 such microscopists who sought to verify the results 



detailed in any article or work on microscopy. The 

 lack of this information very much detracts, in my 

 opinion, from the usefulness of Dr. Carpenter's work 

 on the Microscope, and many other books on the 

 same subject. Science is nothing if it lack precision. 

 —F. J. George. 



Trichina in Pigs. — I think it will interest some of 

 our microscopic friends to see the result of the com- 

 pulsory examinations of pigs for trichina, . before the 

 meat is allowed to be sold, for the town of Berlin, 

 from the 1st of October, 1879, to the 30th of Septem- 

 ber, 1880. The number of pigs examined, 170,981; 

 from which were killed, in public slaughter-houses, 

 51,687 ; in different parts of the town, 119,294. Out 

 of these 143 were found to contain trichina — that is 

 I in 1x95. The number of public examiners in 

 October, 1879, was 243; at the end of September, 

 1880, 184. — Dessau. 



Finishing and Mounting Slides. — In Mr. 

 Ford's communication on " Finishing Slides," I take 

 it that he claims that the ring of Canada balsam dries 

 very quickly so that the slide is " ready for the cabinet 

 within a few minutes ;" if so, I must say that this is 

 quite contrary to my experience. I have finished some 

 dozens of slides in the manner described by Mr. Ford, 

 but always found it necessary to dry the slides off by 

 placing them for some days in a warm place. I have 

 not tried it myself, but I understand that pure gum 

 dammar and benzole is a much better varnish for 

 finishing off slides than Canada balsam in any form, 

 as it dries much more quickly without heat. This 

 plan of finishing slides is a safe one for amateurs, but 

 after all I must say I much prefer the " white cement " 

 which I now invariably use when practicable. With 

 regard to "mounting objects in fluid for the 

 microscope," whilst agreeing in the main with Mr. 

 Lovett's remarks and method, yet I cannot say I am 

 enamoured with his "fluid," which being composed 

 half of absolute alcohol is really as strong as " proof" 

 spirit. What is going to contain this volatile liquid ? 

 I must confess that I am doubtful about the marine 

 glue, seeing that a large bulk of the same is made up 

 of shellac, which also enters largely into the com- 

 position of sealing-wax ; and the solvent of sealing-wax 

 varnish is alcohol — aided it is true, with a little warmth. 

 But why use alcohol or any other volatile fluid for a 

 permanent slide if other preservatives can be found ? 

 The proportion of glycerine in Mr. Lovett's fluid 

 would, I take it, answer his every purpose, glycerine 

 itself acting as a preservative, but if the same be used 

 /tv- se, on account of its density, it is apt to pro- 

 duce distortion of the cell contents ; this, however, I 

 understand can be avoided by placing the objects to 

 soak in a weak solution of glycerine, and gradually 

 increasing its strength from time to time by adding 

 pure glycerine. Of course if Mr. Lovett can mount 

 slides in a strong alcoholic fluid which will last any 



