438 Sorby : On the Prcservafioii of Marine Animals. 



ticulars, since nearly every^ animal requires special treatment, 

 and what is desirable in one case would be ruinous in another. 

 Animals thus mounted as lantern slides form admirable museum 

 specimens, and I have a collection of about 85 species, illus- 

 tratingf the fauna of the Thames estuary, arrang-ed over white 

 paper in a series of shallow trays and drawers, so as to form 

 a very compact and ornamental museum, showing; man}^ facts 

 far better than specimens preserved in alcohol or formalin ; and, 

 besides this, they can be at once examined under a microscope 

 with moderate powers, since it is possible to preserve much of 

 the natural structure. 



In 1899 it occurred to me that some animals might be kept 

 to advantage in liquids of higher refractive power than alcohol, 

 so that they might be more transparent, and the internal struc- 

 ture seen ; and also that some liquid might be found which 

 does not dissolve out or destroy the natural colours like alcohol 

 or formalin do. This has led me into a wide field of research, 

 since it has involved many experiments with colouring matters, 

 and the study of the action on them of light, with or without the 

 combined influence of air. The difference in the behaviour of 

 diff'erent coloured animals in different liquids has been found 

 very remarkable, and, thoug'h the colours are often faded by 

 light, yet in a few cases they are altered in tint and actually 

 made darker. So far the chief liquids employed have been 

 undiluted glycerine and a concentrated solution of lump sugar. 

 What is wanted is some preservative liquid which has no solvent 

 power for the colouring matters or x:hemical action on them. In 

 many cases undiluted glycerine has given most excellent results, 

 though its affinity for water is somewhat too strong. Animals 

 which soon become nearly white in alcohol or formalin have 

 retained their colour more or less perfectly for some years when 

 not exposed to strong sunlight, and, in some cases, even when 

 exposed to it as much as possible. A few, but only a few, pig- 

 ments fade even when kept in the dark, but what is remarkable 

 and requires further study is that in the case of some Crustacea 

 a deep red or orange pigment is developed, or at all events made 

 apparent. In some species this occurs when they are kept in 

 a concentrated solution of sugar, but in others does not, so that 

 the animals remain as when alive, but fade in alcohol or formalin 

 and beconie too dark and falsely coloured in glycerine. For this 

 reason syrup is very good, but it sometimes ferments or turns 

 mouldy in a very puzzling manner, owing to conditions which so 

 far I have been unable to understand. 



