360 PRESERVATION OF MARINE ORGANISMS 



Hermann's Solution. This is similar to Flemming's solution, 

 excepting that i per cent, platinum chloride is used instead 

 of i per cent, chromic acid. The solution is used in the same 

 way as Flemming's solution. It is said to preserve the proto- 

 plasmic structures better than Flemming's fluid. 



Osmic Acid. A very powerful killing agent for small 

 organisms, such as Protozoa or small Crustacea. It is generally 

 used in | per cent, solution. The vapour of the acid is also 

 used, a drop of water containing minute organisms being put 

 in a closed dish in which a few drops of osmic acid solution 

 have been placed. A great disadvantage of osmic acid is 

 that it blackens the specimen very much, especially if the 

 tissue is of a fatty nature ; the blackening can be removed 

 with a weak solution of chlorine, which does not improve the 

 tissues for microscopic work. 



C. ANESTHETICS. 



If put immediately into a fixing fluid many marine animals 

 contract and shrink up. It is therefore necessary, in order to 

 get well-expanded specimens, to anaesthetize before killing. 

 The substances generally used for this purpose are cocaine, 

 menthol, and very weak alcohol. Chloral hydrate is also 

 sometimes used, as well as other anaesthetics. It is to be 

 noted, however, that the methods of anaesthetization are not 

 to be recommended for use in the tropics ; the animals die and 

 rot too quickly in small bodies of water (see p. in). 



Cocaine (hydrochloride of cocaine) is a useful and powerful 

 anaesthetic. A i per cent, solution in distilled water should 

 be made up and a few drops added to the sea water containing 

 the living specimen in a fully expanded condition. It is best 

 to increase the dose at intervals, and not to add the full 

 quantity at once or suddenly. A sudden overdose frequently 

 makes the animal contract ; if it does not show signs of ex- 

 panding within about three minutes, then remove it into a vessel 

 of clean sea water and let it revive. Try next time with less 

 cocaine. 



Solutions of cocaine do not keep very long, and are usually 

 spoilt by fungoid growths. It is advisable not to make up 

 more than 100 c.c. 



Directly the animal becomes anaesthetized pour in the 

 killing or fixing solution. After adding corrosive sublimate or 

 picric acid a precipitate is frequently produced. The pre- 



