ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 879 



smell of the ammonia becomes very faint. The reaction of the vapour 

 is then tried with litmus paper. Sufficient acid has been added when 

 the litmus paper begins to get red. Often, on stirring, the alkaline 

 reaction will return,but this must be removed with another drop ol acetic 

 acid. In use it will be found that with a neutral or slightly acid 

 mass, a diffusion of the medium through the cell-walls is scarcely 

 likely to occur. 



b. As a cold fluid mass, Emery recommends a 10 per cent, carmine 

 solution prepared with ammonia, to which, while continually stirring, 

 acetic acid is added until the carmine begins to be precipitated, and 

 the liquid has a blood-red colour. The clear liquid only must be 

 used, and after injection, the objects must be at once placed in strong 

 alcohol, to fix the carmine. 



c. For injecting the capillaries, good results are often obtained by 

 gradually mixing 10 per cent, carmine solution with acetic acid, 

 until part of the carmine is precipitated. The solution must be 

 shaken shortly before use, only allowing it to settle for a few minutes, 

 so that the coarser grains do not get into the syringe. In injections 

 from the arteries a considerable quantity of fine sediment remains in 

 the capillaries, while only a light fluid enters the veins. Thus the 

 veins can easily be distinguished from the arteries, which are dyed 

 dark red. 



IV. Mounting. — The great object aimed at, in preparing per- 

 manent preparations for the Microscope, is to entirely get rid of the 

 water in the tissues of the object, and supplant it by a preservative 

 medium. Hence, at Naples the aqueous mounting media such as 

 glycerine, glycerine jelly, acetate of potash, &c, are in little favour. 

 After the water has been forced from the object and supplanted by 

 alcohol, the process is usually completed by passing through oil of 

 cloves, and mounting in balsam. Usually there is little trouble with 

 this method. The oil of cloves, or other similar oil, is slightly 

 heated, and as a rule it will penetrate the tissues without trouble. 

 "With larger objects, however, and particularly those with thin but not 

 easily permeable walls, the alcohol will often leave hefore the oil can 

 enter, and there will be a collapse of the walls. Creosote has been 

 used to prevent this shrinking, but it appears to render no permanent 

 good. Dr. Mayer meets the difficulty in the larger objects by making 

 an insertion with a fine pair of scissors in an unimportant part of the 

 body-cavity, so as to allow the oil to ent( r at once. This answers very 

 well, and can be used with very small objects, such as Auricularia 

 and other larva?, if a fine flattened needle be used. If this should 

 fail, and especially when the number of objects to be transferred to 

 balsam is large, the alcohol may be supplanted gradually. Dr. Mayer 

 has thus prepared very young larvae of Echinoderms. The specimens 

 were taken up in a capillary tube, with the surrounding alcohol, and 

 then placed in a tube, with a drop of oil of cloves at the bottom. 

 After the lapse of half-a-day the larvae, which at first swam on the top 

 of the oil, had gone to the bottom of it, and could be easily removed 

 again by the same tube. Objects may be left in oil of cloves for 

 months without any apparent detriment. 



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