FIXING AND PRESERVATIVE MEDIUMS 45 



Amongst the Cephalopoda, Lo Bianco (p. 469) has found 

 that small octopods are readily narcotised by a 2 per thousand 

 solution, followed by their immediate immersion in alcohol, and 

 although occasionally they contract and hide their bodies with 

 their arms, yet after death it is easy to place them in a natural 

 position. 



Small Decapods are managed in like manner, with the in- 

 tervention of alcoholised sea-water (Formula 2) between the 

 chloral hydrate and definitive alcohol. 



Some of the Ascidians, such as Molgula, Polycarpa, Rhopalea, 

 and Chevreulius {Rhodosomd), are left for twelve hours in a 

 I per thousand solution to narcotise them, then killed by 

 the chrom-acetic mixture (Formula 38), and after that hardened 

 for a short time in a i per cent, solution of chromic acid. 



The advantages of these solutions are, that they narcotise 

 various animals, and also that if, after a certain time, an animal 

 does not assume the position desired, it is possible to revive it 

 by replacing it in sea-water, after which it can be re-narcotised in 

 a more favourable position. They are also used for fixing and 

 killing the animals composing colonies of Serpulce and Madre- 

 poria. 



Formal or Formalin ( = 40 per cent, formic aldehyd and 

 60 per cent, water). — This is valuable as an antiseptic, and is 

 also used — usually in the following proportion — as a preserva- 

 tive : — 



31. — Solution for various Preservative Purposes 



Formol . . . 5 parts 



Water (distilled) 95 „ 



This is said to preserve perfectly the form and colours of 

 animals ; it has, however, been tried for some fishes, invertebrata, 

 and marine algae in the Leicester Museum, and, although ap- 

 parently a first-class preservative, it discharged the natural 

 colours at once. It is now being tried with other subjects, and 



