356 PRESERVATION OF MARINE ORGANISMS 



Formol-Alcohol (Formalin Spirit). — This is made by 

 adding 5 per cent, of commercial formol (40 per cent, 

 formaldehyde) to alcohol of 70 per cent., thus : Alcohol 

 70 per cent., 95 ex. ; formaldehyde 40 per cent., 5 c.c. 



Formol-alcohol is one of the best preserving fluids 

 for general collections which are not required for 

 histological work. The specimens are put directly 

 into the fluid, which should be changed after about 

 twenty-four hours. In the case of animals which 

 contract readily, they should be anaesthetized with 

 cocaine, menthol, or weak spirit, before being put into 

 the formol-spirit. 



In cases where it is important to preserve delicate 

 calcareous structures (e.g., Holothurians) this mixture 

 is not recommended, as it may develop an acid re- 

 action. 



B. Fixing Fluids. 



Corrosive sublimate (bichloride of mercury, Hg.Cy 

 is probably the most generally useful fixing fluid, when 

 specimens are required for minute study of their cell- 

 structure. 



It is used either as a simple saturated solution in 

 water, or can be mixed with glacial acetic acid if it 

 is not desired to preserve calcareous structures. For 

 marine animals the following proportions are recom- 

 mended : Bichloride of mercury, saturated solution in 

 distilled water,* 95 c.c. ; glacial acetic acid, 5 c.c. 

 Both the simple saturated solution of sublimate and 



* One hundred cubic centimetres of distilled water will dis- 

 solve 6 or 7 grammes of bichloride of mercury at ordinary 

 temperatures. It is best to add an excess of the bichloride 

 and dissolve in hot water. On board ship it is easiest to have a 

 big bottle, with an inch or two of powdered corrosive sublimate 

 at the bottom, and fill it up with water every night ; it will be 

 saturated by morning if shaken occasionally. 



