[5] PRESERVATION OP MICROSCOPIC MATERIALS. 611 



"■ (4.) This crust also prevents tlie action of staining fluids, except 

 aqueous solutions of the latter, by which it would be dissolved. 



" Notwithstanding these drawbacks, alcohol is still regarded at the 

 Naples Aquarium as an excellent fluid for Txillmg many animals designed 

 for preservation in museums or for histological work. In many cases 

 the unsatisfactory results obtained are to be attributed not to the alco- 

 hol per se, but to the method of using it. Most of the foregoing objec- 

 tions do not, as Dr. Mayer has expressly stated, apply to fresh-water 

 animals ; and Dr. Eisig informs me that he has no better method of 

 killing marine annelids than with alcohol. Judging from the prepara- 

 tions which were kindly shown to me, and which were all beautifully 

 stained with borax- carmine, Dr. Eisig's mode of treatment must be pro- 

 nounced very successful. The process is extremely simple : a few drops 

 of alcohol are put into a vessel which contains the annelid in its native 

 element, the sea water; this is repeated at short intervals until death 

 ensues. After the animal has been thus slowly killed, it may be passed 

 through the different grades of alcohol in the ordinary way (as described 

 above), or through other j)reservative fluids. Objects killed in this man- 

 ner show no trace of the external crust of precipitates which arises where 

 stronger grades of alcohol are first used. The action of the alcohol is 

 thus moderated, and the animal, dying slowly, remains extended and 

 in such a supx)le condition that it can easily be placed in any desired 

 position. The violent shock given to animals when thrown alive into 

 alcohol of forty to sixty per cent, giving rise to wrinkles, folds, and dis- 

 tortions of every kind is thus avoided, together with its bad effects."* 



Acid alcohol. — Dr. Whitman also says, " In order to avoid the bad 

 effects of alcohol, such as precipitates, maceration, etc., Dr. Mayer rec- 

 ommends acid ateo/ioZ, 05 volumes, 70 per cent.; or, 90 jjer cent, alco- 

 hol, 3 volumes hydrochloric acid,t for larger objects, particularly if 

 they are designed for preservation in museums. The fluid should be 

 frequently shaken up, and the object only allowed to remain until thor- 

 oughly saturated, then transferred to pure 70 per cent, or 90 per cent, 

 alcohol, which should be changed a few times in order to remove all 

 traces of the acid. For small and tender objects, acid alcohol, although 

 preferable to pure alcohol, gives less satisfactory results than picro- 

 sulphuric acid." 



" Boiling alcohol. — In some cases among the arthropods, Dr. Mayer 

 has found it difficult to kill immediately by any of the ordinary means, 



* [Embryo fishes may be killed without distortion by exposure to tho fumes of chlo- 

 roform. The embryos are placed iu a -watch-glass iu water, or iu a ring on the plate 

 of a compressorium, when a few drops of chloroform are placed alongside of the watch- 

 glass or ring iUled with the water containing the embryos, and the whole covered with 

 a larger watch-glass or bell-glass, and left a few minutes till the embryos are killed 

 in their fully extended condition. The interesting collembolan, Svuj7ithitrus, may be 

 killed in chloroform or ether with its remarkable bifurcate collophore fully extruded.] 



tAcid alcohol as above prepared loses its original qualities after standing some 

 time, as ctbor poropounds are gradually formed at the expense of the acid. 



