NO. 42.— 1891.] ZOOLOGICAL SPECIMENS. 



69 



the full strength of the gum and glycerine mixture. Many 

 attempts were made to reduce the specific gravity of the 

 glycerine. It may be asked, Why not have tried spirit ? 

 The answer is that some of my very first experiments in this 

 Colony were with mixtures of glycerine and spirit. They 

 are most powerful preservatives, and have the inestimable 

 advantage in this hot climate of not evaporating, or at least 

 not perceptibly ; but they are absolutely destructive to all 

 colour, bleaching the specimens with great rapidity. If 

 watery solutions of salts or acids are used to reduce the 

 specific gravity, a grand crop of fungus springs up at once. 

 The only successful chemical was chloral, but it was soon 

 found that light colours faded in watery solutions almost as 

 soon as in alcoholic preparations. E is an example of a 

 chloralised glycerine solution of about the specific gravity 

 of milk, three years old ; but it is expensive, and has no 

 particular advantage except that it does not evaporate. My 

 next experiments were solutions of gelatine in spirit. This 

 is a very good preservative, but it does not keep bright 

 colours. There is, perhaps, nothing better for frogs, all the 

 delicate folds and glandular lines so important in identifying 

 the species of this very difficult class of animals being 

 preserved as in life. The mixture is made by soaking a 

 packet of Nelson's gelatine in a pint of cold water for ten or 

 twenty minutes, which is sufficient in this climate. Dissolving 

 it by a gentle heat, it is then carefully stirred up with 

 sufficient cold-proof spirit; the mixture should measure 

 about 40 degrees below proof. F is a specimen of a young 

 example of a very rare species of frog prepared in this 

 medium, and mounted in chloralised glycerine. G is another 

 example of a moderately sized frog, mounted in weak 

 spirit, which is a better mounting medium. We have now 

 two processes — one a splendid colour preserver of very 

 limited use, the other an excellent preservative for very 

 delicate objects, but not a preserver of any bright colour, 

 although for dark tints it does very well. I now come to a 

 very difficult subject : What is the action of the gum and 



