ON COLLECTING INVERTEBRATE ANIMALS 105 



Commercial foimalin costs in London 15s. per gallon; accordingly 

 the 10 per cent, solution costs only Is. 6cZ. per gallon. Formalin is 

 excellent for preserving some specimens ; but caution and further 

 experiment as to the use of it are necessary. A collector should 

 not entrust all his specimens to this new preservative, but keep some 

 in alcohol. 



Commercial formalin generally contains a considerable percentage 

 of free acid, and consequently will injure calcified structures, such as 

 molluscan shells, unless the acid has been previously neutralized. 

 This may conveniently be effected by placing a little chalk or pounded 

 coral into the strong solution. 



Before the final preservation of animals in formalin or alcohol, 

 ceitain preliminary measures are necessary, or rather, desirahle. 

 Animals should be killed by means of a reagent which rapidly causes 

 death, prevents contraction, and '' fixes " the tissues as nearly as 

 possible in the position they had duiing life. 



The killing and fixing reagents most commonly used are chromic 

 acid, osmic acid, and corrosive sublimate; after employing them, it 

 is necessary to wash the animals in fresh or distilled water before 

 placing them in formalin or alcohol. In the case of soft contractile 

 organisms it is necessary to narcotize them first before attempting 

 to kill, in order to prevent distortion. A solution of chloral hydrate, 

 varying from 1 per cent, to 1 in 1,000 in sea-water or fresh-water, is 

 often used for this purpose. Lo Bianco recommends immersion in 

 weak alcohol. He generally uses a mixture of sea- water 100 ccm., 

 and absolute alcohol 5 ccm. In other cases 70 per cent, alcohol 

 may be carefully poured upon water in which the specimen lies, so 

 that it forms a layer at the surface. It will gradually mix with 

 the subjacent water, and in the course of a few hours will narcotize 

 the animal, so that it may be treated with fixing reagents without 

 fear of contraction. Tobacco smoke is employed for Actinice. Dr. 

 Sorby has obtained beautiful results by poisoning with menthol. 



Co7'rosive Sublimate. — A saturated solution in fresh- or sea-water 

 may be used either hot or cold. It acts quickly, and preserves 

 admirably for histological purposes. It is especially good combined 

 with copper sulphate, acetic acid, or chromic acid. Objects hardened 

 in it should be subsequently well w^ashed in distilled water and in 



