26 



CHAPTE14 III. 



alcohol causes precipitates that may ruin the preparations. 

 Objects fixed in alcohol, forniol, acetic acid, picric acid, or 

 nitric acid require to be washed out v/ith alcohol, or at least 

 with some hardening liquid, whilst those that have been 

 fixed with osmic or chromic acid, or with one of the other 

 compounds of the heavy metals, require in general to be 

 washed out with water. Sublimate, however, is best washed 

 out with alcohol. 



Use liberal quantities of liquid for washing. 



Change the liquid as often as it becomes turbid, if that 

 should happen. 



1'he process of washing out is greatly facilitated by heat. 

 Picric acid, for instance, is nearly twice as soluble in alcohol 

 warmed to 40°C. as in alcohol at the normal temperature (Fol). 



32. Fixation of Marine Animals. — The tissues of marine 

 organisms are as a general rule more refractory to the action 

 of reagents than those of corresponding fresh-water or terres- 

 trial forms, and fixing solutions should in consequence be 

 stronger (about two to three times). 



Marine animals ought to he freed from the sea v:ater adhe- 

 rent to their surface before treating them either with alcohol 

 or any fixing reagent that precipitates the salts of sea water. 

 If this be not done, the precipitated salts will form on the 

 surfaces of the organisms a crust that prevents the penetra- 

 tion of reagents to the interior. Fixing solutions for marine 

 organisms should therefore be such as serve to keep in a 

 state of solution, and finally remove, the salts in question. 

 If alcohol be employed, it should be acidified with hydro- 

 chloric or some other appropriate acid. Picro-nitric acid is 

 a fixing reagent that fulfils the conditions here spoken of. 

 (On this subject see Mayee, in Mitlh. Zool. Stat. Neajwl, ii 

 (1881), p. 1, et seq.) 



33, Hardening, — The process of hardening is distinguished 

 from that of fixing as being directed to the attainment of a 

 degree of consistency suflficient to allow of soft tissues being 

 cut into sections without imbedding. It is an after-process, 

 and only ranks as a special method. 



Methods of imbedding have now been brought to such a 

 degree of perfection that the thorough hardening of soft 

 tissues that was formerly necessary in order to cut thin 



