1>REPARING MINUTE ORGANISMS. 89 



elements come out also prominently. Spongillce^ HydrcB^ small 

 Nematodes, delicate Insect-larvae, the ciliated gills of Mussels, 

 etc., may all be excellently fixed and preserved. But to make 

 these preparations durable, it is absolutely needful that the fixing 

 fluid be removed when it has completed its work, as it might 

 otherwise injure or decompose the organisms by longer action. 



Professor Entz then describes his method of procedure in the 

 following terms, which we borrow from " The Journal of the 

 Royal JMicroscopical Society," vol. II., p. 121 : — "I place the 

 Protozoa or other microscopical organisms, together with the 

 Algae^ sediment, or other objects to which they are attached, with 

 some water in a watch-glass, and then drop in a few drops of the 

 fixing fluid, which I allow to act only one to tivo mumtes. I then 

 pour off the fluid carefully, or simply lift the preparation out w4th 

 a pencil, in order to transfer it at once into a larger quantity of 

 alcohol, which must not be too strong. Half-an-hour is usually 

 enough to withdraw the fixing fluid and replace it by the alcohol, 

 in which it may remain for a longer time without damage. For 

 removing the chlorophyll colouring-matter of many Infusoria, 

 and also of the x\lgse in the preparation, a longer stay in alcohol 

 is of course necessary, replacing this by clear alcohol when it has 

 become coloured. 



" Microscopical organisms thus treated may then be mounted 

 at once in equal parts of glycerine and distilled water. But 

 colouring must not be neglected. Carmine certainly is to be 

 preferred, because it is not bleached in glycerine, and does not 

 colour everything with one tint like the aniline dyes, but prin- 

 cipally the nuclear elements. Preparations transferred from 

 alcohol to carmine are mostly coloured sufficiently in ten to 

 twenty minutes ; only loricated forms, such as Etigle?ia. Spiro- 

 §yra, the PeridinccE^ etc., require several hours to make their nuclei 

 sufficiently prominent. To remove superfluous dye, the prepara- 

 tions must, of course, be put into distilled water before being 

 transferred to the glycerine : they should remain in it until the 

 yellow picric acid is drawn out, and only a nice rose-colour 

 remains. 



" Beautiful and instructive preparations may thus be obtained, 

 which when carefully mounted show no further change. I have a 

 fairly considerable collection of different Protozoa, which have not 

 altered in the least for six or seven months, and are adapted both 

 for demonstration and for detailed study." 



